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Prochlorococcus

Prochlorococcus is a genus of unicellular marine cyanobacteria that is the smallest and most abundant photosynthetic prokaryote on Earth, thriving in the nutrient-poor (oligotrophic) surface waters of the world's oceans between approximately 40°S and 40°N latitude.^[1] These microbes, with cell diameters of 0.5–0.7 μm, were discovered in 1988 during oceanographic studies off the coast of Barbados using flow cytometry techniques.^[1] Prochlorococcus cells can reach densities of up to 10^5 to 10^6 per milliliter in the euphotic zone, making them a dominant component of marine picophytoplankton and contributing 50% or more to primary production in certain oceanic regions.^[2] Their global population is estimated at around 3 × 10^27 cells, underscoring their ecological ubiquity and numerical dominance among oxygenic phototrophs.^[3] Ecologically, Prochlorococcus plays a pivotal role in global biogeochemical cycles, accounting for roughly 20% of the ocean's total primary productivity and thus a substantial fraction—up to 5%—of Earth's overall photosynthesis, which helps regulate atmospheric CO₂ levels and supports marine food webs.^[3] Recent models suggest that rising ocean temperatures could reduce its global production by 10–37% by the end of the 21st century.^[4] Unlike many cyanobacteria that use phycobilisomes for light harvesting, Prochlorococcus employs unique divinyl chlorophyll a and b-containing antennae complexes, enabling efficient adaptation to low-light conditions in the deep euphotic zone.^[5] This pigmentation and streamlined physiology, including a compact genome of 1.7–2.4 megabase pairs with around 2,000 genes, allow them to thrive in environments with limited nutrients and irradiance, where they fix carbon and produce oxygen essential for planetary habitability.^[6] The genus exhibits remarkable genetic and physiological diversity, organized into distinct ecotypes such as high-light-adapted (HL) and low-light-adapted (LL) strains, which partition niches based on depth, temperature, and nutrient availability across latitudinal gradients.^[2] This "collective diversity" forms a pan-genome exceeding 80,000 genes through horizontal gene transfer and phage interactions, enhancing resilience to environmental stressors like viral lysis and grazing by protists.^[3] Basal lineages retain ancestral phycobilisomes, suggesting evolutionary adaptations from anoxic conditions, while modern strains influence not only current ocean ecosystems but also potentially ancient oxygenation events.^[5] As a model organism for microbial oceanography, Prochlorococcus continues to reveal insights into prokaryotic evolution, viral ecology, and climate regulation.^[2]

Discovery and Taxonomy

Discovery

Prochlorococcus was first detected in 1985 by Sallie W. Chisholm and her colleagues during oceanographic studies off the coast of Barbados using flow cytometry techniques. These cells, measuring less than 1 μm in diameter, exhibited a distinct red autofluorescence indicative of chlorophyll, distinguishing them from other known marine microbes. The discovery highlighted a previously unrecognized component of the oceanic microbial community in oligotrophic waters.^[7]^[1] In 1988, the first culture of Prochlorococcus was isolated from a 120-meter depth in the Sargasso Sea by Ben Palenik under Chisholm's team at the Massachusetts Institute of Technology; this strain, designated SS120, marked a pivotal step in studying the organism in controlled conditions. That same year, Chisholm et al. published the initial description of these cells as a novel free-living prochlorophyte, noting their high abundance in the deep euphotic zone, often exceeding 10^5 cells per milliliter. The formal taxonomic description as Prochlorococcus marinus nov. gen. nov. sp. followed in 1992, solidifying its status as a distinct genus within the cyanobacteria.^[1]^[7] Initial studies quickly recognized Prochlorococcus's remarkable abundance and its potential to play a major ecological role in marine primary production, particularly in nutrient-poor regions where it often dominated the picophytoplankton assemblage. Early observations suggested it could contribute substantially to carbon fixation in subtropical oceans, with global population estimates later refined to approximately 2.9 × 10^{27} cells (annual mean abundance), underscoring its biogeochemical significance.^[8]^[9] Chisholm's groundbreaking work on Prochlorococcus was honored with the 2019 Crafoord Prize in Biosciences by the Royal Swedish Academy of Sciences, awarded for the discovery and pioneering studies of this most abundant photosynthesizing organism on Earth.^[10]

Taxonomy

Prochlorococcus is classified within the domain Bacteria, phylum Cyanobacteriota, class Cyanophyceae, order Synechococcales, family Prochlorococcaceae, and genus Prochlorococcus.^[11] The genus comprises marine picocyanobacteria characterized by their small cell size and oxygenic photosynthesis, first formally described in 1992 based on isolates lacking phycobiliproteins and instead containing divinyl forms of chlorophylls a and b. This pigmentation distinguishes Prochlorococcus from its close relative Synechococcus, which relies on phycobilisomes for light harvesting rather than chlorophyll b-containing antennas.^[12] Phylogenetic analyses using 16S rRNA sequences and multi-gene alignments indicate that Prochlorococcus represents a distinct prochlorophyte lineage that diverged from other cyanobacteria under low-oxygen conditions, predating the divergence from marine Synechococcus clades. This evolutionary history highlights its adaptation to low-oxygen marine environments. The genus maintains a monophyletic position within the cyanobacterial radiation, supported by conserved genomic signatures such as reduced genome sizes and specialized pigment systems.^[5]^[13] The sole formally recognized species is Prochlorococcus marinus, encompassing diverse strains isolated from oligotrophic ocean waters, with no additional species elevated to formal status despite extensive genomic surveys.^[14] Subclades within P. marinus are delineated as ecotypes based on light adaptation and niche specialization, but these remain informal groupings rather than distinct species under current bacteriological nomenclature.^[15] Post-2010 phylogenomic studies, leveraging whole-genome comparisons and average amino acid identity metrics, have reinforced the close phylogenetic affinity of Prochlorococcus to marine Synechococcus while affirming its unique evolutionary trajectory as a streamlined oceanic primary producer.^[15]

Morphology and Cell Structure

Cell Morphology

Prochlorococcus cells exhibit a coccoid morphology, appearing as small, spherical prokaryotes with diameters typically ranging from 0.5 to 0.7 μm.^[16]^[17] These non-motile cells lack flagella or other appendages, relying instead on passive dispersal through ocean currents.^[16]^[18] As the smallest known oxygenic phototroph, this diminutive size enables Prochlorococcus to dominate in nutrient-poor marine environments.^[19]^[20] The compact cell structure provides a high surface-area-to-volume ratio, which facilitates efficient uptake of scarce nutrients in oligotrophic waters.^[1] Prochlorococcus cells also lack gas vacuoles, further streamlining their design for minimal resource use without mechanisms for buoyancy regulation.^[1] Ultrastructurally, Prochlorococcus features a Gram-negative cell envelope with an outer membrane and a thin peptidoglycan layer.^[21] The thylakoid membranes, numbering 2 to 6 per cell, are tightly appressed and arranged in concentric rings or horseshoe configurations parallel to the cytoplasmic membrane, optimizing space for photosynthesis in the constrained cellular volume.^[22]^[1] Under phosphate-limited conditions, common in open ocean habitats, Prochlorococcus replaces phosphorus-containing phospholipids in its membranes with sulfoquinovosyldiacylglycerol (SQDG), a sulfur-based lipid that constitutes up to 66% of total membrane lipids and reduces phosphorus demand.^[23] This lipid remodeling enhances survival by conserving phosphorus for essential cellular processes.^[23]

Pigment Composition

Prochlorococcus utilizes divinyl chlorophylls a and b (Chl a₂ and Chl b₂) as its primary photosynthetic pigments, which are unique among oxygenic phototrophs due to the presence of vinyl groups on the C8 position of the porphyrin ring, shifting their absorption maxima by 8–10 nm toward longer wavelengths compared to monovinyl chlorophylls.^[1] These pigments enable efficient absorption of blue (Chl b₂ peaks at ~472 nm) and red (Chl a₂ at ~675 nm) light, optimizing energy capture in the oligotrophic ocean environment where blue light predominates. Unlike most cyanobacteria, such as the co-occurring Synechococcus, most Prochlorococcus strains lack phycobilisomes—large, nitrogen-rich extramembranous complexes—and instead employ intrinsic membrane-bound light-harvesting complexes (LHCs) composed of Pcb (prochlorophyte chlorophyll a/b-binding) proteins associated with Chl a₂ and Chl b₂.^[5]^[1] These Pcb antennae, with molecular masses of 32.5–38 kDa, facilitate energy transfer to photosystems I and II, supporting a streamlined photosynthetic apparatus.^[24] Accessory pigments in Prochlorococcus include zeaxanthin and α-carotene, which provide photoprotection by dissipating excess energy as heat under high-light conditions, preventing photooxidative damage.^[1] Zeaxanthin predominates in high-light-adapted strains, while trace amounts of a Chl c-like pigment (Mg-3,8-divinyl pheoporphyrin a₅ monomethyl ester) may occur, though its functional role remains minor. Pigment ratios vary significantly across ecotypes adapted to different light regimes: high-light strains exhibit low Chl b₂/Chl a₂ ratios (0.1–0.6), favoring narrower absorption spectra suited to surface waters, whereas low-light strains display higher ratios (>1.1), enhancing light harvesting in deeper, dimmer layers by broadening absorption into the green spectrum.^[25] This variability arises from differential expression of Pcb genes and allows acclimation to irradiance gradients without structural reorganization.^[26] The absence of phycobiliproteins in most strains represents an evolutionary innovation in Prochlorococcus, enabling oxygenic photosynthesis with reduced nitrogen demands, as phycobilisomes in other cyanobacteria incorporate nitrogen-intensive chromophores and proteins.^[27] This adaptation, likely arising from early divergence under nutrient-limited conditions, minimizes cellular nitrogen allocation to pigmentation while relying on chlorophyll-based antennae for equivalent efficiency. Such streamlining contributes to the organism's dominance in nitrogen-poor oceanic gyres.^[1]

Distribution and Habitat

Global Distribution

Prochlorococcus is a cosmopolitan marine cyanobacterium predominantly distributed in the euphotic zone of tropical and subtropical oceans, spanning latitudes from approximately 40°N to 40°S. It thrives in warm, oligotrophic waters and is notably absent from polar regions and high-nutrient coastal areas, such as upwelling zones, where cell abundances drop to medians of around 10^4 cells mL^{-1}. Peak abundances, reaching up to 2.8 × 10^5 cells mL^{-1}, occur in nutrient-poor subtropical gyres, including the Sargasso Sea in the Atlantic and the central gyres of the Pacific and Indian Oceans.^[9]^[1] Vertically, Prochlorococcus dominates from the ocean surface to depths of about 200 m, with detectable populations extending deeper in low-light conditions, though abundances decrease below 150 m. Different ecotypes exhibit preferences within this stratified range, contributing to its overall prevalence in the upper water column. The global population is estimated at approximately 3 × 10^{27} cells, accounting for roughly 50% of the chlorophyll content—and thus a substantial portion of photosynthetic picoplankton biomass—in vast oligotrophic surface ocean regions.^[9] Spatial and seasonal variations in Prochlorococcus distribution are tracked using satellite-derived chlorophyll data from instruments like SeaWiFS and MODIS, combined with in situ measurements from oceanographic cruises and time-series stations. Abundances are generally higher during periods of thermal stratification, such as summer in subtropical gyres, with global maxima observed in April (around 3.0 × 10^{27} cells) compared to minima in August (2.7 × 10^{27} cells). These patterns reflect its adaptation to stable, low-nutrient environments across the open ocean.^[9]

Environmental Conditions

Prochlorococcus is observed in surface waters from approximately 10°C to 32°C, with optimal growth rates between 24°C and 28°C; laboratory studies show growth limits from about 12°C to 30°C, beyond which division rates decline sharply; the organism is particularly sensitive to rapid temperature fluctuations, which can disrupt its physiological processes.^[4]^[28]^[1] This cyanobacterium exhibits a strong preference for oligotrophic waters characterized by low nutrient levels, where it maintains high growth rates under nitrogen or phosphorus limitation; elevated concentrations, such as those exceeding typical open-ocean thresholds, inhibit its proliferation by altering metabolic balances and favoring competitors.^[1]^[29] Prochlorococcus demonstrates salinity tolerance between 25 and 40 parts per thousand (ppt), reflecting its adaptation to the stable, high-salinity conditions of open marine environments, though exposure to extremes beyond this range induces stress responses affecting gene expression and survival.^[30]^[31] Adapted to the low-light conditions of the oceanic euphotic zone, Prochlorococcus ecotypes exhibit photosynthetic saturation at irradiances of 0.1–100 μmol photons m⁻² s⁻¹, enabling dominance in deeper, dimly lit waters; it employs pigment compositions and cellular strategies for UV protection, minimizing damage from ultraviolet radiation in surface layers.^[1]^[32] Prochlorococcus flourishes in oxygenated surface waters with a pH range of 7.5–8.5, where its carbon fixation efficiency is optimized through cytosolic pH regulation and reliance on ambient oxygen levels above a minimum threshold of approximately 36 μM to support photosynthetic metabolism.^[33]^[34]

Genome and Genetics

Genome Structure

The genome of Prochlorococcus is a single circular chromosome, characteristically small and streamlined, making it the smallest known among free-living oxygenic phototrophs. Typical genome sizes range from 1.7 to 2.4 megabase pairs (Mbp), encoding approximately 1,700 to 2,500 genes, which reflects extensive gene loss and optimization for nutrient-poor marine environments.^[35] High-light-adapted ecotypes, such as the MED4 strain, possess even more compact genomes around 1.66 Mbp with about 1,884 protein-coding genes, while low-light-adapted ecotypes like MIT9313 have larger genomes of approximately 2.41 Mbp.^[36] A core genome of roughly 1,273 genes is conserved across Prochlorococcus strains, representing essential functions for basic cellular processes, with the remainder consisting of variable genes often in hypervariable regions. This streamlining involves the loss of non-essential genes, such as those for nitrate reductase in many strains, enabling reliance on alternative nitrogen sources like ammonium and organic compounds. The overall gene content exhibits high efficiency, with a GC content of 30–35% that favors AT-rich sequences, contributing to a pronounced codon usage bias toward optimal, translationally efficient codons.^[37]^[38]^[39] Evidence of horizontal gene transfer (HGT) is prominent, with approximately 5–10% of genes showing signatures of foreign origin, including acquisitions from viruses (such as photosynthetic genes) and eukaryotes (like fructose-1,6-bisphosphate aldolase). These HGT events, often localized in genomic islands, enhance adaptability to environmental stresses without substantially increasing genome size.^[40]^[41]

DNA Repair and Replication Mechanisms

DNA replication in Prochlorococcus is initiated by the DnaA protein, which binds to the origin of replication (oriC) to unwind the DNA and facilitate the assembly of the replisome, leading to bidirectional replication forks that proceed around the circular chromosome.^[42] This process is tightly synchronized with the diel light-dark cycle, with initiation occurring in the afternoon under light conditions to support the organism's photosynthetic lifestyle.^[43] The replication rate is high, typically completing one full genome duplication per cell cycle, aligning with division rates of up to one doubling per day in optimal oligotrophic conditions.^[44] Prochlorococcus employs several DNA repair systems adapted to the oxidative and UV stresses of the marine surface environment. The RecBCD pathway plays a key role in homologous recombination, processing double-strand breaks by unwinding and degrading DNA ends to generate single-stranded tails for strand invasion and repair.^[45] Error-prone repair is mediated by the UmuCD complex, which functions in translesion synthesis during the SOS response to bypass DNA lesions at the cost of potential mutations.^[45] The LexA repressor regulates these stress responses by binding to SOS boxes and derepressing repair genes upon DNA damage detection via RecA activation.^[45] UV-induced damage, prevalent due to Prochlorococcus' surface ocean habitat, is primarily reversed by photolyase enzymes that utilize blue light energy to split cyclobutane pyrimidine dimers formed between adjacent thymine or cytosine bases.^[46] Strains such as MED4 exhibit hyper-resistance to UV, attributed to a single base pair deletion upstream of an operon encoding a nudix hydrolase and photolyase, leading to their constitutive overexpression and efficient repair of UV-induced damage.^[46] This mechanism ensures genome integrity under high solar exposure, preventing lethal mutations from thymine dimers. Recombination frequency in Prochlorococcus is elevated in certain genomic regions, particularly hypervariable islands, where the ratio of recombination to mutation (r/m) can exceed 1, facilitating rapid adaptation to environmental pressures through allelic exchange. The RecBCD system contributes to this by promoting homologous recombination, which integrates beneficial variants while maintaining core genome stability.^[45] Such dynamics support ecotype divergence without overall high gene flux. The mutation rate in Prochlorococcus is low at approximately 1.6 × 10^{-10} per base pair per generation, reflecting a streamlined repair apparatus that balances fidelity with the selective pressures of nutrient-poor habitats.^[47] This rate, lower than in many bacteria, is counteracted by recombination to sustain genetic diversity across its global population.^[47]

Metabolism

Photosynthetic Metabolism

Prochlorococcus performs oxygenic photosynthesis through the coordinated action of photosystems I (PSI) and II (PSII), facilitating linear electron transport that generates ATP via proton translocation across the thylakoid membrane and NADPH through ferredoxin reduction.^[48] This process mirrors that in other cyanobacteria but is optimized for the oligotrophic marine environment, where light and nutrient availability are limited.^[48] The minimal cellular architecture of Prochlorococcus, including a reduced number of photosynthetic complexes, supports efficient energy capture without excessive energy loss.^[5] The photosynthetic quantum yield in Prochlorococcus is notably high, approaching approximately 0.1 mol O₂ evolved per mol photon absorbed, which is close to the theoretical maximum for oxygenic photosynthesis.^[49] This efficiency stems from the organism's exceptionally small light-harvesting antenna, comprising divinyl chlorophylls a/b and minimal accessory pigments, which reduces package effect losses and enhances light utilization in the low-irradiance subsurface ocean. Such adaptations allow Prochlorococcus to maintain high photosynthetic rates even at photon fluxes below 10 μmol m⁻² s⁻¹, contributing significantly to global primary production.^[48] Carbon fixation in Prochlorococcus is catalyzed by form IA RuBisCO, a large-subunit enzyme with relatively low affinity for CO₂ (K_c ≈ 750 μM), which is well-suited to the low dissolved inorganic carbon (DIC) concentrations typical of open-ocean surface waters.^[50] Encapsulated within α-carboxysomes, this RuBisCO benefits from a streamlined CO₂-concentrating mechanism (CCM) that elevates local CO₂ levels to approximately 100 times ambient concentrations, compensating for the enzyme's kinetic limitations and minimizing photorespiration.^[51] This setup enables sustained carboxylation under DIC-limiting conditions prevalent in stratified gyres. Photoprotection in Prochlorococcus involves non-photochemical quenching (NPQ) mechanisms that dissipate excess absorbed energy as heat, primarily mediated by the carotenoid zeaxanthin, whose intracellular levels increase under high-light exposure to quench chlorophyll excitation.^[52] Unlike higher plants, Prochlorococcus lacks a full xanthophyll cycle but exhibits rapid, reversible NPQ with capacities up to 0.5-1.0, particularly in high-light-adapted strains, preventing oxidative damage during diurnal light fluctuations.^[53] This zeaxanthin-dependent quenching integrates with the small antenna size to balance energy flow and maintain PSII integrity.^[54] Excess photosynthetic products in Prochlorococcus are stored primarily as glycogen, a β-glucan polymer, rather than polyhydroxyalkanoates like poly-β-hydroxybutyrate (PHB), as the genome lacks the necessary pha genes for PHB synthesis.^[55] Glycogen pools can accumulate to 20-40 fg per cell under nutrient-replete conditions, serving as a dynamic carbon reserve that supports nighttime metabolism and transient energy demands without compromising the streamlined genome.^[56] This storage strategy aligns with the organism's minimalistic physiology, prioritizing rapid turnover over long-term sequestration.^[56]

Carbon and Nutrient Metabolism

Prochlorococcus exhibits an incomplete tricarboxylic acid (TCA) cycle, lacking succinate dehydrogenase, which prevents the full oxidation of succinate to fumarate and limits the cycle's role in energy production.^[57] Instead, the organism relies on alternative pathways for carbon assimilation, including the use of α-ketoglutarate dehydrogenase (or related decarboxylase/ferredoxin oxidoreductase) to generate succinyl-CoA for anaplerotic reactions, supporting the replenishment of TCA intermediates during nutrient-limited conditions. This streamlined metabolism optimizes resource use in oligotrophic oceans, where carbon fixed via the Calvin-Benson-Bassham cycle is directed toward biosynthesis rather than complete respiration.^[58] Nitrogen assimilation in Prochlorococcus primarily occurs through the glutamine synthetase-glutamate synthase (GS-GOGAT) pathway, utilizing ammonium as the preferred substrate to form glutamate, which serves as a nitrogen donor for amino acid synthesis.^[59] Most strains lack nitrate reductase genes, rendering them incapable of reducing nitrate to ammonium, though some low-light-adapted ecotypes possess nitrite reductase for limited nitrite utilization.^[59] This adaptation reflects the prevalence of ammonium in the euphotic zone and minimizes energy expenditure on less accessible nitrogen sources. Phosphate acquisition is facilitated by high-affinity ABC transporters encoded by the pstABCS operon, which are upregulated under phosphorus starvation to scavenge low concentrations of orthophosphate in nutrient-poor waters.^[60] Under phosphate limitation, Prochlorococcus remodels its membrane lipids by substituting phospholipids with sulfoquinovosyldiacylglycerol (SQDG), a sulfur-containing lipid that reduces phosphorus demand while maintaining membrane integrity.^[61] Iron and trace metal uptake occurs via siderophore-independent ABC transporters, such as the Fut system, which binds both Fe(II) and Fe(III) ions directly, enabling efficient acquisition in iron-scarce environments without reliance on exogenous chelators.^[62] Cellular growth yields in Prochlorococcus are modest, with an average carbon content of approximately 25–50 fg per cell, reflecting its minimalistic cell size and streamlined genome.^[63] Doubling times range from 0.5 to 2 days under optimal laboratory conditions, varying with light, temperature, and nutrient availability in natural settings.^[1]

Ecology

Role in Marine Ecosystems

Prochlorococcus plays a pivotal role in marine primary production, particularly in oligotrophic gyres where it fixes a substantial portion of organic carbon, often accounting for 50–90% of net primary production in subtropical gyre regions.^[64] Globally, this cyanobacterium is estimated to contribute approximately 4 Gt of carbon per year, representing about 8.5% of total ocean net primary production.^[9] Through its photosynthetic activity, Prochlorococcus generates a significant amount of oxygen, contributing up to 20% to Earth's atmospheric oxygen supply via marine photosynthesis.^[65] In marine food webs, Prochlorococcus occupies a basal position as a key primary producer, serving as prey for mixotrophic protists such as Ochromonas and other grazers that consume it to supplement their nutrition.^[66] It is also heavily infected by cyanophages, specialized viruses that lyse cells and regulate population dynamics, thereby facilitating nutrient release and carbon transfer to higher trophic levels.^[63] Carbon fixed by Prochlorococcus contributes to export from surface waters through incorporation into sinking particles, supporting the biological carbon pump and deep-ocean sequestration.^[67] Prochlorococcus influences nutrient cycling by assimilating and recycling nitrogen and phosphorus, with rapid cell turnover via grazing and viral lysis returning these elements to dissolved pools for reuse by other microbes.^[68] Additionally, Prochlorococcus co-occurs with heterotrophic bacteria in particle-attached aggregates, where these bacteria enhance aggregation and protect against oxidative stress, promoting collective carbon export.^[69]

Climate Change Impacts

Ocean warming, driven by anthropogenic climate change, poses a significant threat to Prochlorococcus populations through direct thermal stress and indirect effects on ocean stratification. Recent global ecosystem modeling indicates that under moderate warming scenarios (RCP4.5), Prochlorococcus production in tropical regions could decline by 17% by 2100, escalating to a 51% reduction under high-emission scenarios (RCP8.5), primarily due to increased temperatures exceeding the organism's optimal range of 20–30°C and enhanced stratification that suppresses nutrient upwelling from deeper waters.^[4] Globally, these projections suggest a 10–37% decrease in overall biomass production, potentially diminishing oceanic primary productivity by 3–10% and altering carbon sequestration dynamics.^[4] Such declines could cascade through marine food webs, reducing the availability of this foundational primary producer for higher trophic levels.^[70] Ocean acidification, resulting from elevated atmospheric CO₂ levels, exerts both direct and indirect influences on Prochlorococcus. Directly, increased CO₂ availability enhances the efficiency of RuBisCO-mediated carbon fixation by reducing photorespiration, as the higher CO₂:O₂ ratio favors carboxylation over oxygenation, potentially boosting growth rates in low-light-adapted ecotypes by alleviating oxidative stress.^[71] Indirectly, acidification reduces calcification in marine grazers and competitors, such as certain zooplankton and coccolithophores, which may lower grazing pressure and competitive exclusion, allowing Prochlorococcus to proliferate in more nutrient-limited surface waters.^[72] However, these benefits could be offset by heightened vulnerability to oxidative damage under combined acidification and warming, as heterotrophic bacterial partners that mitigate reactive oxygen species decline.^[73] Shifts in nutrient availability due to intensified stratification from warming are expected to initially favor Prochlorococcus, given its adaptation to oligotrophic conditions, but may lead to long-term declines. Enhanced thermal stratification inhibits vertical mixing and nutrient upwelling, creating more nutrient-depleted surface layers that suit Prochlorococcus's low-nutrient affinity, potentially increasing its relative abundance in subtropical gyres in the near term.^[74] Over longer horizons, however, extreme oligotrophy could limit growth if iron or phosphorus becomes critically scarce, exacerbating declines already projected from warming.^[75] Increased ultraviolet (UV) radiation from ozone depletion strains Prochlorococcus' DNA repair systems, though inherent protective mechanisms offer some resilience. Projected rises in UVB penetration due to stratospheric ozone loss could overwhelm nucleotide excision repair pathways, reducing cell viability and productivity in surface waters.^[76] While Prochlorococcus lacks robust mycosporine-like amino acid production, its streamlined genome supports efficient photolyase-mediated repair, mitigating UV-induced damage to photosynthetic apparatus.^[32] Post-2020 observations from initiatives like the Tara Oceans expedition extensions and GO-SHIP repeat hydrography cruises document early signs of poleward range expansion for Prochlorococcus, consistent with warming-induced habitat shifts. These surveys reveal increased abundances in mid-latitude waters (30–40°N/S), where temperatures are rising into the organism's tolerance range, suggesting a broadening distribution despite tropical contractions.^[77] Such expansions could enhance carbon export in higher latitudes but underscore the need for ongoing monitoring to resolve model-observation discrepancies.^[78]

Ecotypes and Diversity

Low-Light Adapted Ecotypes

Low-light adapted ecotypes of Prochlorococcus dominate the deeper euphotic zone, particularly clades LLI, LLII/III, and LLIV, which are phylogenetically distinct from high-light adapted forms and exhibit larger genomes averaging around 2.4 Mb in size for LLIV, with LLI and LLII/III falling intermediately between high- and low-light extremes. These ecotypes possess higher cellular content of divinyl chlorophyll b relative to divinyl chlorophyll a, enabling enhanced absorption of blue light that penetrates to depths of 80–200 m where they thrive.^[24] This pigmentation shift supports their niche in the lower euphotic zone, where light intensity is reduced but nutrient availability can be higher due to remineralization.^[5] Key adaptations in low-light ecotypes include expanded antenna complexes composed of multiple prochlorophyte chlorophyll-binding (Pcb) proteins, with up to seven pcb genes in strains like SS120, facilitating efficient light harvesting under dim conditions compared to the streamlined single pcb gene in high-light types.^[26] Additionally, these ecotypes retain genes encoding high-affinity transporters for nutrients such as iron and phosphorus, which are absent or reduced in high-light adapted strains, allowing scavenging of trace elements in nutrient-variable deep waters.^[79] Such genomic features underscore their specialization for oligotrophic but light-limited environments. In terms of abundance, low-light ecotypes reach concentrations of approximately 10^4 cells/mL within the deep chlorophyll maximum layer, contributing significantly to subsurface primary production, and they exhibit seasonal blooms in stratified oceanic waters during periods of stable thermal layering in late summer.^[80]^[81] Physiologically, they display slower growth rates, with population doubling times of 1–2 days under optimal low-light conditions, reflecting their adaptation to subdued irradiance rather than rapid surface proliferation.^[82] Despite this, they achieve higher quantum yields of photosynthesis in low light, optimizing energy capture efficiency, though their maximum photosynthetic rates remain lower than those of high-light counterparts.^[52] Genomically, low-light ecotypes retain functional genes for glycerol uptake, including glycerol kinase, enabling utilization of organic carbon sources that may supplement autotrophy in nutrient-scarce depths, a capability often lost in streamlined high-light lineages.^[38] They also preserve genes for alternative electron sinks, such as flavodiiron proteins, which mitigate excess reducing power under fluctuating low-light regimes and prevent photooxidative damage.^[29] These retained elements highlight the evolutionary trade-offs favoring versatility over minimalism in deeper niches.

High-Light Adapted Ecotypes

High-light adapted ecotypes of Prochlorococcus are specialized for the illuminated surface waters of the ocean, typically occupying depths from 0 to 100 m where irradiance levels are intense. These ecotypes are primarily represented by clades HLI and HLII, with HLII dominating in abundance, particularly in subtropical and tropical regions. HLI strains, such as the type strain MED4, exhibit optima for cooler temperatures compared to HLII, which thrives in warmer conditions above 20°C.^[83]^[84]^[85] Genomes of high-light adapted ecotypes are notably compact, averaging around 1.7 Mb with approximately 1,700 genes, enabling a streamlined lifestyle suited to nutrient-scarce environments. These ecotypes feature reduced chlorophyll b content relative to chlorophyll a, minimizing energy investment in light-harvesting complexes optimized for low irradiance. Instead, they rely on elevated zeaxanthin levels, which facilitate non-photochemical quenching and provide protection against excess blue and UV light prevalent in surface layers. Genomic streamlining includes the loss of genes like petH, which encodes ferredoxin:NADP⁺ reductase and is dispensable under high-light conditions where alternative electron transfer pathways suffice. Additionally, these ecotypes possess fewer nutrient transporters, reflecting adaptations to the oligotrophic conditions of clear, warm surface waters.^[86]^[24]^[52]^[87] In terms of abundance, high-light ecotypes can reach up to 10⁵ cells mL^-1 in the upper mixed layer, forming the bulk of Prochlorococcus populations in stratified, low-nutrient gyres. Physiologically, they support faster growth rates than low-light counterparts, with doubling times of approximately 1 day under optimal high-irradiance conditions, enabling rapid proliferation in sunlit zones. Their robust photoprotective mechanisms, including zeaxanthin-mediated dissipation, confer resilience to UV exposure but result in lower photosynthetic efficiency when light is dim. Despite chronic UV stress at the surface, these ecotypes maintain low overall mutation rates, on the order of 10^-10 per site per generation, supported by efficient DNA repair systems.^[88]^[89]^[32]^[90]

Strains and Clades

Prochlorococcus strains are primarily isolated from oligotrophic ocean regions, with key laboratory strains including MIT9313, belonging to the low-light adapted clade IV (LLIV), isolated in 1992 from 135 m depth in the Gulf Stream, Atlantic Ocean; MED4, from the high-light adapted clade I (HLI), isolated in 1988 from the Mediterranean Sea; and SS120, from the low-light adapted clade LLII/III, isolated in 1988 from approximately 120 m depth in the Sargasso Sea, Atlantic Ocean.^[91] These strains, obtained between 1988 and the early 2000s, represent foundational isolates used in physiological and genetic studies, often through flow cytometry sorting or dilution techniques from surface or deep waters in the Atlantic and Pacific Oceans.^[92] The genetic diversity of Prochlorococcus is organized into six major clades—HLI, HLII, and the low-light clades LLI through LLIV—with clades LLIII and LLIV being rarer and typically found in specific nutrient-limited or deeper environments.^[87] These clades are defined primarily by variations in the internal transcribed spacer (ITS) sequences of the ribosomal RNA operon, which reveal phylogenetic relationships and ecotypic adaptations.^[93] Clade assignments, such as MIT9313 to LLIV and MED4 to HLI, enable targeted research into light and nutrient responses across the species.^[94] Laboratory cultivation of Prochlorococcus strains typically employs axenic media formulated with low nutrient concentrations, such as Pro99 or AMP1, to mimic oligotrophic conditions, with illumination adjusted to 2–40 µmol photons m⁻² s⁻¹ depending on the clade.^[95] Maintaining low-light adapted strains like MIT9313 presents challenges, including slow growth rates and susceptibility to chlorosis under nutrient or light stress in pure cultures, often necessitating co-cultivation with marine heterotrophs like Alteromonas to facilitate robust colony formation and long-term viability.^[96]^[95] These strains serve as models in genomic research, with the 2003 sequencing of MED4, MIT9313, and SS120 providing the first cyanobacterial pangenome insights by revealing a core genome of about 1,273 genes shared across isolates alongside variable accessory genes that drive ecotypic specialization.^[91] Additionally, strains like MED4 and MIT9313 are widely used as hosts in phage studies, enabling isolation and genomic analysis of cyanomyoviruses and podoviruses that infect Prochlorococcus, which inform viral-mediated gene transfer and population dynamics.^[97] Post-2015 isolates have expanded the known physiological range, such as the high-light clade II strain RSP50, isolated from the Gulf of Aqaba in the Red Sea around 2016, which demonstrates adaptation to elevated temperatures up to 30°C and high salinity, highlighting thermal extremes in warm marine environments.^[98] More recently, as of 2023, four novel low-light adapted strains were isolated from below the deep chlorophyll maximum in the North Pacific Ocean, further expanding insights into their macroevolution and physiological diversity.^[52]

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A novel free-living prochlorophyte abundant in the oceanic euphotic ...
Jul 1, 1988 · Published: 01 July 1988. A novel free-living prochlorophyte abundant in the oceanic euphotic zone. Sallie W. Chisholm,; Robert J. Olson ...
[7]
The marine prochlorophyte Prochlorococcus contributes significantly ...
Chisholm (submitted) Comparative ecology of Prochlorococcus and Synechococcus strains from the subtropical ocean: Regulation of growth and pigmentation by light ...
[8]
Present and future global distributions of the marine Cyanobacteria ...
The global mean annual abundance for Prochlorococcus and Synechococcus was 2.9 ± 0.1 × 1027 and 7.0 ± 0.3 × 1026 cells, respectively. The highest/lowest global ...
[9]
Sallie W. Chisholm - Crafoord Prize
Crafoord Prize - Biosciences 2019. Citation “for the discovery and pioneering studies of the most abundant photosynthesising organism on Earth, ...
[10]
Taxonomy browser Taxonomy Browser (Prochlorococcus) - NCBI
THE NCBI Taxonomy database allows browsing of the taxonomy tree, which contains a classification of organisms.
[11]
Independent evolution of the prochlorophyte and green ... - PNAS
Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently.
[12]
Genome divergence in two Prochlorococcus ecotypes ... - Nature
Aug 13, 2003 · Here we compare the genomes of two Prochlorococcus strains that span the largest evolutionary distance within the Prochlorococcus lineage.
[13]
Prochlorococcus marinus - NCBI
THE NCBI Taxonomy database allows browsing of the taxonomy tree, which contains a classification of organisms.
[14]
Genomic Taxonomy of the Genus Prochlorococcus | Microbial Ecology
Aug 21, 2013 · Our aim was to analyze the taxonomic structure of the genus Prochlorococcus. We analyzed the complete genomes of 13 cultured P. marinus type and reference ...Missing: 2013 | Show results with:2013
[15]
Prochlorococcus | Request PDF - ResearchGate
Cells are small non‐motile cocci that possess no known extracellular appendages. The major core lipids of cell membranes are sulfolipids and glycolipids.
[16]
Prochlorococcus, a marine photosynthetic prokaryote of global ...
The minute photosynthetic prokaryote Prochlorococcus, which was discovered about 10 years ago, has proven exceptional from several standpoints.
[17]
Prochlorococcus marinus (1) | PDF | Biology | Nature - Scribd
Prochlorococcus marinus is a coccoid, non-motile, free- living marine ... with a simple structure: a thin cell wall, DNA fibrils, carboxysomes for ...
[18]
Genome divergence in two Prochlorococcus ecotypes reflects ...
The marine unicellular cyanobacterium Prochlorococcus is the smallest-known oxygen-evolving autotroph. It numerically dominates the phytoplankton in the ...
[19]
Single cell genomes of Prochlorococcus, Synechococcus, and ...
Sep 4, 2018 · Although Prochlorococcus cells have the smallest genomes of known oxygenic phototrophs (~1.6–2.7 Mbp and ~2000–3000 genes), the global ...<|control11|><|separator|>
[20]
Cryo-Electron Tomography Reveals the Comparative Three ...
Evolution of a reduced cell wall in Prochlorococcus MED4. Striking differences exist in the cell wall ultrastructure of the Prochlorococcus MED4 strain.
[21]
IMMUNOLOGICAL AND ULTRASTRUCTURAL ...
However, thylakoids were concentrically arranged in the strain from the Sargasso Sea (SARG) and horseshoe-shaped in the Mediterranean isolate (CCMP 1378).
[22]
Sulfolipids dramatically decrease phosphorus demand by ... - NIH
... limits on the amount of phosphorus dedicated to lipid synthesis by Prochlorococcus. ... membrane lipids in Prochlorococcus were either sulfolipids or ...Missing: wall | Show results with:wall
[23]
[PDF] The photosynthetic apparatus of Prochlorococcus
Comparison of the phycoerythrin-encoding genome regions in Prochlorococcus MIT 9313, SS120 and MED4 compared to Syn- echococcus WH 8020. This region is framed ...Missing: Ben | Show results with:Ben
[24]
Resolution of Prochlorococcus and Synechococcus Ecotypes by ...
By examining a wide range of physiologically diverse isolates of Prochlorococcus and marine cluster A Synechococcus, we lay the groundwork for informed studies ...Missing: Ben | Show results with:Ben
[25]
Multiplication of antenna genes as a major adaptation to low light in ...
3A) shows that the TAK9803–2 strain has a high ratio of divinyl-Chl a to b, which is characteristic of all high-light-adapted Prochlorococcus strains, whereas ...
[26]
Nitrogen cost minimization is promoted by structural changes in the ...
Jun 6, 2017 · Prochlorococcus is a globally abundant marine cyanobacterium with many adaptations that reduce cellular nutrient requirements, ...
[27]
Future ocean warming may cause large reductions in ... - Nature
Sep 8, 2025 · We created an in silico warm-adapted strain with an increased thermal tolerance to evaluate the potential impacts of Prochlorococcus populations ...
[28]
Transcriptional Mechanisms of Thermal Acclimation in ...
Apr 13, 2023 · Low temperature limits the growth and the distribution of the key oceanic primary producer Prochlorococcus, which does not proliferate above ...
[29]
Dynamic Allocation of Carbon Storage and Nutrient-Dependent ...
... growth became limited by phosphate or nitrogen. Since Prochlorococcus is known to thrive in oligotrophic ocean gyres where nitrogen or phosphate is limited ...
[30]
Global transcriptome analysis of salt acclimated Prochlorococcus ...
The results presented here provide the first glimpse into global gene expression changes in Prochlorococcus cells due to salt stress.Missing: early | Show results with:early
[31]
Acclimation and stress response of Prochlorococcus to low salinity
Oct 12, 2022 · This study demonstrated the growing salinity range of Prochlorococcus cells and their global gene expression changes due to low salinity stress.Missing: ppt | Show results with:ppt<|separator|>
[32]
Ultraviolet stress delays chromosome replication in light/dark ...
Jul 29, 2010 · ... mycosporine-like amino acids synthesis [58]. However, no evidence for such a UV sensor is available in Prochlorococcus and, as argued later ...
[33]
pH determines the energetic efficiency of the cyanobacterial CO2 ...
Aug 22, 2016 · We predict an optimal cytosolic pH range of 7.5–8.5 for carbon-fixing cyanobacteria. At pH 7.7 the total energetic cost of fixing carbon ...
[34]
A low oxygen threshold for physiological responses and trace metal ...
Jul 25, 2025 · However, hypoxic conditions (36 μM O2) significantly inhibited the growth of Prochlorococcus MIT9313, suggesting a minimum O2 threshold needed ...
[35]
Genomes of diverse isolates of the marine cyanobacterium ... - Nature
Sep 30, 2014 · The marine cyanobacterium Prochlorococcus is the numerically dominant photosynthetic organism in the oligotrophic oceans, and a model system ...
[36]
Genome sequence of the cyanobacterium Prochlorococcus marinus ...
It contains 1,884 predicted protein-coding genes with an average size of 825 bp, a single rRNA operon, and 40 tRNA genes. Together with the 1.66-Mbp genome of P ...Missing: structure | Show results with:structure
[37]
Patterns and Implications of Gene Gain and Loss in the Evolution of ...
The core genome of Prochlorococcus, with 81% of the 1,273 genes having an inferred function, is now reasonably well understood and appears to encode a viable ...
[38]
Patterns and Implications of Gene Gain and Loss in the Evolution of ...
We compare the genomes of 12 strains of Prochlorococcus representing its major lineages in order to identify genetic differences affecting the ecology of ...<|separator|>
[39]
Accelerated evolution associated with genome reduction in a free ...
Jan 14, 2005 · ... Prochlorococcus genomes. Using a rate of 16S rRNA divergence of 1% per 50 million years [37], one can estimate that the differentiation of ...Missing: billion | Show results with:billion
[40]
Transfer of photosynthesis genes to and from Prochlorococcus viruses
Here we report the presence of genes central to oxygenic photosynthesis in the genomes of three phages from two viral families (Myoviridae and Podoviridae)Missing: percentage | Show results with:percentage
[41]
Horizontal transfer of a eukaryotic plastid-targeted protein gene to ...
The phylogeny of class I FBA shows the Prochlorococcus/Synechococcus genes originated once, and strongly suggests this was by horizontal gene transfer from a ...
[42]
Unique organization of the dnaA region from ... - PubMed
In order to study DNA replication control elements in cyanobacteria we cloned and sequenced the dnaA gene from the marine cyanobacterium Prochlorococcus marinus ...Missing: mechanisms | Show results with:mechanisms
[43]
Diel Expression of Cell Cycle-Related Genes in Synchronized ... - NIH
To understand the underlying molecular mechanisms we cloned and sequenced dnaA and ftsZ, two key cell cycle-associated genes, and studied their expression. An ...
[44]
Growth of Prochlorococcus, a Photosynthetic Prokaryote ... - Science
DNA replication occurred in the afternoon and cell division occurred at night. Growth rates were maximal (about one doubling per day) at 30 meters and decreased ...
[45]
Comparative Genomics of DNA Recombination and Repair in ... - NIH
Nov 9, 2016 · In addition to these core genes, the marine Prochlorococcus and Synechococcus strains harbor recBCD (DNA recombination), umuCD (mutational DNA ...
[46]
UV hyper-resistance in Prochlorococcus MED4 results from a single ...
Using visible light, especially in the blue-violet range, as a source of energy, photolyases catalyse the repair of cyclobutane dipyrimidine dimers formed by UV ...
[47]
Prochlorococcus have low global mutation rate and small effective ...
Dec 23, 2021 · A genome-reduced Prochlorococcus member has a very low unbiased global mutation rate. We managed a 1,065-day propagation of this strain on ...
[48]
Prochlorococcus, a Marine Photosynthetic Prokaryote of Global ...
Some of its photosynthetic properties may giveProchlorococcus a definite selective advantage for growth at depth in oligotrophic areas, particularly compared ...Characterization And... · Physiology · Genome Size And Base...
[49]
Vertical distributions and photosynthetic action spectre of two ...
The photosynthetic quantum yield ofP. marinus was higher than that ofSynechococcus sp. at any wavelength between 400 and 700 nm. The calculated in situ ...
[50]
Kinetic isotope effect and biochemical characterization of form IA ...
Sep 27, 2007 · Purified enzyme had a pH optimum of 7.5, was most active between 20°C and 30°C, had a moderate Vmax (0.41 µmol min−1 mg protein−1), and had the ...
[51]
Novel isolates expand the physiological diversity of Prochlorococcus ...
Prochlorococcus is a diverse picocyanobacterial genus and the most abundant phototroph on Earth. Its photosynthetic diversity divides it into high-light ...
[52]
The occurrence of rapidly reversible non‐photochemical quenching ...
Dec 8, 2004 · We show here that in fact the ecologically important marine prochlorophyte, Prochlorococcus, is capable of forming rapidly reversible non- ...
[53]
Photoinactivation of Photosystem II in Prochlorococcus and ... - NIH
Jan 27, 2017 · PSII photochemistry can lead to charge separation and electron transport, parameterized as the yield ΦPSII, or to fast recombinations resulting ...
[54]
Prochlorococcus Cells Rely on Microbial Interactions Rather than on ...
Aug 11, 2020 · Prochlorococcus relies on co-occurring heterotrophic bacteria to survive extended phases of nutrient and light starvation.
[55]
https://journals.asm.org/doi/10.1128/mbio.01846-20
[56]
https://pmc.ncbi.nlm.nih.gov/articles/PMC7900632
[57]
Metabolic evolution and the self-organization of ecosystems - PNAS
Mar 27, 2017 · We examined how metabolic evolution shapes ecosystems by reconstructing it in the globally abundant oceanic phytoplankter Prochlorococcus.
[58]
Streamlined Regulation and Gene Loss as Adaptive Mechanisms in ...
In much the same way as nitrite, urea is utilized by some (55, 63) but not all Prochlorococcus isolates (e.g., SS120 lacks the ure cluster [8]), indicating the ...
[59]
Phosphate acquisition genes in Prochlorococcus ecotypes
Here we examine adaptations to phosphate (P) limitation among ecotypes. First, we used DNA microarrays to identify genes involved in the P-starvation response.Missing: SQDG | Show results with:SQDG
[60]
Error | Proceedings of the National Academy of Sciences
Insufficient relevant content. The provided content from https://www.pnas.org/doi/10.1073/pnas.0602980103 is a 404 Page Not Found error page with no substantive information on lipid remodeling to SQDG under phosphate limitation in Prochlorococcus. It contains only error messaging, metadata, and periodic table elements, none of which relate to the requested topic.
[61]
A redox switch allows binding of Fe(II) and Fe(III) ions in the ... - PNAS
The majority of the Prochlorococcus species lack genes for siderophore biosynthesis (18, 19); instead, the bacterium relies on the Fut ABC transporter for iron ...
[62]
Light-driven synchrony of Prochlorococcus growth and mortality in ...
Prochlorococcus cell production and mortality rates are tightly synchronized to the day/night cycle across the subtropical Pacific Ocean.
[63]
[PDF] Phytoplankton Contributions to Marine Net Primary Productivity and ...
The majority of NPP within the five subtropical gyre regions is contributed by Prochlorococcus. (fraction of NPP ∼0.50–0.90), with a general western ...
[64]
Strain-Specific Differences in the Grazing Sensitivities of Closely ...
On the other hand, grazing protection against Ochromonas has been demonstrated for an ultramicrobacterial strain (19). ... linked the observed 16S rRNA ...
[65]
Adaptive carbon export response to warming in the Sargasso Sea
Mar 8, 2022 · The cyanobacteria genera Synechococcus and Prochlorococcus contribute substantially to particulate carbon export, resulting in an overall ...<|control11|><|separator|>
[66]
A Synthesis of Viral Contribution to Marine Nitrogen Cycling - Frontiers
In this review, we summarize viral contributions in the marine nitrogen cycling in different aspects and discuss challenges and issues.<|control11|><|separator|>
[67]
Unveiling the link between phytoplankton molecular physiology and ...
Jun 4, 2025 · Specifically, the growth of Prochlorococcus MED4 is limited by phosphorus in the central Atlantic and the Indian oceans (Fig. 2B). This aligns ...
[68]
Heterotrophic Bacteria Enhance the Aggregation of the Marine ...
Aug 13, 2019 · The contribution of Prochlorococcus and Synechococcus to POC export remains unsettled due to their slow sinking rates as a result of their small ...
[69]
Ocean warming puts vital marine microbe at risk | UW News
Sep 8, 2025 · Instead, a new study finds that Prochlorococcus prefers water between 66 and 86 degrees and doesn't tolerate it much warmer. Climate models ...Missing: pH 7.5– 8.5 oxygenated
[70]
Response of Prochlorococcus to varying CO 2 :O 2 ratios - Nature
Apr 7, 2015 · Given the ability of Prochlorococcus populations to grow under a wide range of oxygen concentrations in the ocean, we wondered how carbon ...
[71]
[PDF] An Updated Synthesis of the Impacts of Ocean Acidification on ...
Note that decreased calcification under conditions of ocean acidification is unlikely ... Around CO2 vents, invertebrate grazing pressure is reduced; however,.
[72]
The impact of elevated CO2 on Prochlorococcus and microbial ...
Oct 31, 2017 · Prochlorococcus may be more vulnerable to oxidative stress under elevated CO 2 in part from a decrease in ecosystem services provided by heterotrophs like ...Missing: oxygenated | Show results with:oxygenated
[73]
Projected Changes in Photosynthetic Picoplankton in a Warmer ...
Jan 14, 2019 · Moreover, the results obtained predict an increase in the dominance, as the percentage of picoautotrophic biomass, of the genus Prochlorococcus.
[74]
Water column stratification governs picophytoplankton community ...
Climate warming further inhibits mixing, which reduces upward nutrient supply and lowers productivity, thereby worsening the situation in oligotrophic oceans.
[75]
Living in a high CO2 world: impacts of global climate change on ...
Increased global warming also has implications for ozone depletion and the consequent increases in UVB radiation incident on the surface of the oceans. This ...
[76]
Understanding opposing predictions of Prochlorococcus in a ...
Mar 15, 2023 · As the temperature warms dynamical models predict that the range of small-celled Prochlorococcus will expand while its concentration decreases.<|separator|>
[77]
Prochlorococcus - Ocean Carbon & Biogeochemistry
Apr 1, 2022 · Prochlorococcus is the world's smallest phytoplankton (microscopic plant-like organisms) and the most numerous, with more than ten septillion individuals.
[78]
Emergence of trait variability through the lens of nitrogen ... - eLife
Feb 1, 2019 · ... Prochlorococcus clades is more likely dominated by gene loss. Low nucleotide diversity among nitrate assimilation genes within clades ...
[79]
Abundance (×10⁴ cells ml⁻¹) of (A) Synechococcus, (B ...
Abundance (×10⁴ cells ml⁻¹) of (A) Synechococcus, (B) Prochlorococcus, (C) picoeukaryotes, (D) total prokaryotes, and (E) percentage of high nucleic acid ...
[80]
Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and ...
May 13, 2010 · To better understand the temporal and spatial dynamics of Prochlorococcus populations, and how these populations co-vary with the physical ...Missing: phylogenomics | Show results with:phylogenomics
[81]
Influence of Light and Temperature on Prochlorococcus Ecotype ...
Aug 10, 2025 · Given that Prochlorococcus is estimated to double every 2.8 ± 0.8 d at the low temperatures in this region 12 , we estimate that 21-51% of the ...
[82]
[PDF] Prochlorococcus: Advantages and Limits of Minimalism
Sep 28, 2009 · Prochlorococcus minimizes resources by reducing cell and genome sizes, giving it an advantage, but this strategy has limits in very ...
[83]
Prochlorococcus Stock Cultures - The Chisholm Lab - MIT
Prochlorococcus Stock Cultures ; MED4, HLI, Mediterranean Sea ; MED4ax, HLI, Mediterranean Sea ; MIT9107, HLII, Tropical Pacific ; MIT9116, HLII, Tropical Pacific ...
[84]
High vertical and low horizontal diversity of Prochlorococcus ...
We used several molecular techniques to study the genetic diversity of natural Prochlorococcus populations during the Prosope cruise in the Mediterranean Sea ...
[85]
CUL-4 ubiquitin ligase maintains genome stability by restraining DNA-replication licensing - Nature
**Summary of Genomic Differences Between High-Light and Low-Light Adapted Prochlorococcus Strains (MED4 and MIT9313 Ecotypes):**
[86]
[PDF] Prochlorococcus: the structure and function of collective diversity
Chisholm, S. et al. A novel free-living prochlorophyte abundant in the oceanic euphotic zone. Nature 334, 340–343 (1988).
[87]
Code and context: Prochlorococcus as a model for cross-scale biology
Prochlorococcus cells are found in abundance – typically 104–105 per ml ... HL cells can grow at light intensities that are great enough to inhibit LL cells ...Missing: maximum | Show results with:maximum
[88]
Variable but persistent coexistence of Prochlorococcus ecotypes ...
Jan 7, 2016 · This study has provided the first formal assessment how the relative abundance of two dominant ecotypes, eMED4 and eMIT9312, varies as a ...
[89]
Genome reduction occurred in early Prochlorococcus with an ... - NIH
Jan 10, 2024 · In the oligotrophic sunlit ocean, the most abundant free-living planktonic bacterial lineages evolve convergently through genome reduction.Missing: billion | Show results with:billion
[90]
Genome sequence of the cyanobacterium Prochlorococcus marinus ...
Aug 13, 2003 · Genomes of a high-light-adapted strain, P. marinus MED4, and another low-light-adapted strain, P. marinus MIT9313, have also recently been ...
[91]
Resolution of Prochlorococcus and Synechococcus Ecotypes by ...
Cultured isolates of Prochlorococcus have been divided into two genetically and physiologically distinct groups, referred to as ecotypes because their ...Missing: formal | Show results with:formal
[92]
[PDF] Prochlorococcus: the structure and function of collective diversity
Dec 1, 2014 · Prochlorococcus has the smallest genome of any free-living phototroph6; some isolates have genomes as small as 1.65 Mbp, with only ~1,700 genes7 ...<|control11|><|separator|>
[93]
Phosphate acquisition genes in Prochlorococcus ecotypes - PNAS
Here we examine adaptations to phosphate (P) limitation among ecotypes. First, we used DNA microarrays to identify genes involved in the P-starvation response.<|separator|>
[94]
Facilitation of Robust Growth of Prochlorococcus Colonies and ...
While the Prochlorococcus cultures tested in this assay were not axenic, the contaminants did not affect the assay, since Prochlorococcus grew only where the ...
[95]
Prochlorococcus Cells Rely on Microbial Interactions Rather than on ...
Aug 11, 2020 · ... phycobilisomes in parallel with an increase in the storage ... Contrasting mechanisms of proteomic nitrogen thrift in Prochlorococcus.
[96]
Three Prochlorococcus Cyanophage Genomes: Signature Features ...
An analysis of the genome sequences of three phages capable of infecting marine unicellular cyanobacteria Prochlorococcus reveals they are genetically complex.
[97]
The genome of a novel isolate of Prochlorococcus from the Red Sea ...
Sep 5, 2018 · Numbers on branches are relative times of divergence between lineages. The scale indicates divergence time of genes (Million Years Ago).Missing: billion | Show results with:billion