Fact-checked by Grok 2 weeks ago

Propionibacterium freudenreichii

Propionibacterium freudenreichii is a Gram-positive, rod-shaped, non-motile, non-spore-forming bacterium belonging to the phylum Actinomycetota, known for its role as a key microorganism in the dairy industry and its potential probiotic applications.^[1] It exhibits slow growth with a generation time of approximately 5 hours, low nutritional requirements, and tolerance to various environmental stresses, including those in the digestive tract.^[1] Primarily isolated from dairy sources such as Emmental cheese, it naturally inhabits environments like milk, silage, soil, the rumen of ruminants, and the human colon.^[1] In cheese production, P. freudenreichii serves as a ripening agent in Swiss-type cheeses, fermenting lactic acid into propionic acid, acetic acid, and carbon dioxide, which imparts the characteristic nutty flavor and contributes to the formation of the cheese's distinctive eyes through gas production.^[1] Additionally, it is a prolific producer of cobalamin (vitamin B12), making it valuable for nutritional fortification in fermented foods.^[2] The bacterium holds Generally Recognized as Safe (GRAS) status from the U.S. FDA and Qualified Presumption of Safety (QPS) from the European Food Safety Authority, underscoring its safety for food and probiotic use.^[1] Beyond its industrial significance, P. freudenreichii demonstrates probiotic properties, including survival under gastrointestinal conditions and modulation of immune responses.^[3] Strain-specific anti-inflammatory effects have been observed, such as the inhibition of pro-inflammatory cytokines like IL-8 and IL-12 while promoting anti-inflammatory IL-10 production in human peripheral blood mononuclear cells.^[3] These effects are mediated by surface layer proteins (e.g., SlpB and SlpE) and metabolites like propionate and 1,4-dihydroxy-2-naphthoic acid (DHNA), with in vivo studies showing alleviation of conditions like colitis in animal models.^[3] Its genome, approximately 2.7 million base pairs with a G+C content of 67%, encodes genes supporting propionic acid fermentation, stress resistance, and vitamin biosynthesis, further highlighting its adaptability and biotechnological potential.^[1]

Taxonomy and Nomenclature

Classification

Propionibacterium freudenreichii is classified within the domain Bacteria, phylum Actinomycetota, class Actinomycetia, order Propionibacteriales, family Propionibacteriaceae, genus Propionibacterium, and species P. freudenreichii.^[4] This Gram-positive, high-GC-content actinobacterium is distinguished by its rod-shaped morphology and propionic acid production.^[5] The species encompasses two subspecies: P. freudenreichii subsp. freudenreichii, which ferments lactose but lacks nitrate reductase activity, and P. freudenreichii subsp. shermanii, which reduces nitrate but does not ferment lactose.^[6] These subspecies reflect adaptations to dairy environments, with subsp. shermanii often predominant in cheese production due to its stress tolerance.^[7] Phylogenetically, P. freudenreichii belongs to the dairy propionibacteria clade, closely related to cutaneous species like those formerly in Propionibacterium but separated by habitat-specific genomic features, including genes for lactose metabolism and vitamin biosynthesis suited to fermented milk.^[8] Its GC content is 66.0–67.3 mol%, aligning it with other Actinomycetota.^[9] Originally described by van Niel in 1928 as a propionic acid-producing bacterium from Swiss cheese, the taxonomy was emended by Moore and Holdeman in 1970 to establish the subspecies based on biochemical traits.^[10] Modern genomic analyses, particularly a 2016 reclassification and a 2018 emendation, have further delineated dairy propionibacteria from cutaneous ones by transferring skin-associated species to genera like Cutibacterium and Acidipropionibacterium, while retaining P. freudenreichii in Propionibacterium due to its distinct phylogenetic position.^[11]^[9]

Etymology

The genus name Propionibacterium is derived from the New Latin neuter noun acidum propionicum (propionic acid) and the Latinized Greek noun bakterion (small rod), reflecting the organisms' production of propionic acid as a primary metabolic end product.^[12] The prefix "propioni-" in turn originates from the Greek words prōtos (πρῶτος, meaning "first") and piōn (πίων, meaning "fat"), as propionic acid (CH₃CH₂COOH) was recognized as the shortest-chain fatty acid beyond acetic acid.^[13] The species epithet freudenreichii honors Edouard von Freudenreich, a Swiss bacteriologist who first isolated the bacterium from cheese in the early 20th century.^[10] The name Propionibacterium freudenreichii was validly published and described by Cornelis B. van Niel in his 1928 monograph on propionic acid bacteria, establishing its taxonomic authority.^[10] Van Niel's work played a key role in the early classification of propionibacteria by linking their metabolic traits to dairy fermentations.^[10]

Morphology and Physiology

Cell Structure

Propionibacterium freudenreichii is a Gram-positive bacterium, featuring a thick peptidoglycan layer in its cell wall that contributes to its structural integrity and resistance properties.^[14] This bacterium is non-spore-forming and non-motile, lacking flagella or pili, which aligns with its classification within the phylum Actinomycetota (class Actinobacteria).^[15]^[16] The cells exhibit a pleomorphic morphology, typically appearing as rods that are 0.2–1.5 µm wide and 1–5 µm long, though they can assume coccoid forms or club-shaped appearances.^[17] These rods often occur singly, in pairs, or in short chains, with occasional chains extending up to 20 µm in length, facilitating colony formation in dairy environments.^[17] Intracellularly, P. freudenreichii contains DNA with a high GC content, averaging approximately 67%, which is characteristic of actinobacterial genomes and influences its genetic stability.^[18] Surface proteins, such as SlpB, are prominent on the cell envelope and mediate adhesion to host tissues or substrates, enhancing its probiotic interactions.^[19]

Growth and Metabolism

Propionibacterium freudenreichii is a facultative anaerobe capable of growth under both anaerobic and microaerobic conditions.^[20] Its optimal growth occurs at temperatures between 30°C and 37°C and at a pH range of 6.0 to 7.0, with growth ceasing below pH 4.5.^[21] Lactate serves as the primary carbon source, supporting robust proliferation in dairy environments.^[22] The metabolism of P. freudenreichii centers on the Wood-Werkman pathway, a key propionic acid fermentation route that converts lactate into valuable end products. In this cycle, the net reaction is represented as:

$3 \text{ lactate} \to 2 \text{ propionate} + 1 \text{ acetate} + 1 \text{ CO}_2 + 1 \text{ ATP}

This pathway generates propionic acid, which imparts flavor, along with acetic acid and carbon dioxide, the latter contributing to gas production.^[23] The bacterium ferments a range of substrates, including sugars such as glucose and lactose, as well as polyols like glycerol and erythritol, enabling versatile carbon utilization.^[24] Nutritionally, P. freudenreichii requires vitamins including biotin and pantothenate for growth, reflecting its auxotrophic needs in these areas.^[1] Under anaerobic conditions, it synthesizes vitamin B12 (cobalamin), which functions as a cofactor in the methylmalonyl-CoA mutase step of the Wood-Werkman pathway.^[25]

History

Discovery

Propionibacterium freudenreichii was first isolated in 1906 from samples of Emmental cheese during studies on the fermentation processes occurring in Swiss-type cheeses. The bacterium was identified by Danish microbiologist Sigurd Orla-Jensen and Swiss researcher Eduard von Freudenreich, who were investigating the microbial agents responsible for propionic acid production in ripening cheese. Their work highlighted the organism's role in the characteristic maturation of Emmental cheese, marking the initial recognition of this species in the context of dairy microbiology.^[14] Early investigations by von Freudenreich and Orla-Jensen linked P. freudenreichii to the production of propionic acid, which contributes to the formation of the distinctive "eyes" (gas bubbles) and nutty flavor profile in Emmental cheese through the fermentation of lactic acid into propionate, acetate, and carbon dioxide. These findings established the bacterium as a key player in the secondary fermentation phase of cheese ripening, distinguishing it from primary lactic acid bacteria. Described as a Gram-positive, non-motile rod adapted to dairy environments, it was noted for its specific association with milk-based fermentations, setting it apart from other propionic acid-producing microbes found in silage or soil.^[1]^[26] The formal taxonomic naming of Propionibacterium freudenreichii occurred in 1928 by microbiologist Cornelis B. van Niel, who classified it within the genus Propionibacterium based on its metabolic properties, particularly its ability to ferment carbohydrates to propionic acid under anaerobic conditions. Van Niel's monograph on propionic acid bacteria provided a comprehensive description, honoring the original discoverers in the species epithet and solidifying its scientific identity as a dairy-specific actinobacterium. This classification laid the groundwork for subsequent microbiological research on the species.^[10]

Industrial Development

Propionibacterium freudenreichii was first adopted in the early 20th century as a starter culture in Swiss-type cheese production, particularly for Emmental, to promote consistent ripening, flavor development through propionate and acetate production, and eye formation via carbon dioxide generation.^[14] This marked its transition from a natural isolate in dairy environments to a controlled industrial agent, leveraging its robust growth under cheese ripening conditions.^[27] In the mid-20th century, industrial processes advanced with the development of targeted strain selection and preservation techniques to enhance performance and viability. Strains were selected for traits such as stress tolerance, metabolic efficiency, and consistent metabolite output, while methods like freeze-drying and spray-drying, often supplemented with protectants like trehalose, enabled long-term storage of viable cultures for reliable starter production.^[14] These innovations standardized P. freudenreichii as a key component in dairy fermentation, ensuring scalability and reproducibility in commercial cheesemaking. The bacterium's safety profile, built on decades of use, led to its recognition as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration.^[27] From the late 20th century into the 21st, P. freudenreichii expanded beyond traditional dairy applications into probiotic formulations and biotechnology, driven by its health-promoting properties and metabolic versatility. Key milestones include the complete genome sequencing of strain CIRM-BIA1 in 2010, which revealed genetic bases for probiotic traits and enabled targeted strain engineering for improved vitamin B12 production and stress resistance.^[28] This genomic insight facilitated its integration into functional foods and bioprocesses, broadening its industrial footprint while maintaining its GRAS and Qualified Presumption of Safety (QPS) statuses.^[27]

Role in Food Production

Cheesemaking

Propionibacterium freudenreichii is typically inoculated into cheese milk at concentrations of 10^3 to 10^6 colony-forming units per milliliter (CFU/mL), depending on the cheesemaking technology, alongside lactic acid bacterial starters during the initial stages of Swiss-type cheese production.^[29]^[30]^[31] This bacterium demonstrates remarkable thermotolerance, enabling it to survive the curd cooking step where temperatures reach 50–55°C for up to 60 minutes, ensuring viable cells persist into the ripening phase.^[32]^[33] During cheese ripening, P. freudenreichii undergoes anaerobic growth in the warm room phase, typically lasting 2–3 months at 20–24°C, where it ferments lactate—produced earlier by lactic starters—into propionate, acetate, and carbon dioxide (CO₂).^[34]^[35] This metabolic activity is central to the development of the cheese's distinctive attributes, as the accumulated CO₂ diffuses through the cheese matrix to form characteristic "eyes," which are spherical holes measuring 1–3 cm in diameter. Additionally, propionic acid imparts the nutty flavor profile typical of these cheeses while exerting antimicrobial effects that inhibit spoilage organisms, such as molds.^[33]^[36] The bacterium is essential for the production of iconic Swiss-type cheeses, including Emmental and Gruyère, where its incorporation defines the product's texture and sensory qualities.^[33] Strain-specific variations in P. freudenreichii can significantly influence eye formation and aroma compound profiles, allowing cheesemakers to tailor outcomes for desired eye size and flavor intensity.^[37]

Other Fermented Products

Propionibacterium freudenreichii serves as an inoculant in silage and fodder production, where it enhances preservation by fermenting lactate to produce propionic acid, which inhibits fungal growth and reduces dry matter losses during storage.^[38] This application mirrors its role in cheesemaking by contributing to acid-based stability in fermented matrices, though adapted for forage ensiling with lactic acid bacteria.^[39] Studies on corn silage demonstrate that inoculating with P. freudenreichii alongside Lactobacillus plantarum improves fermentation efficiency and aerobic stability, minimizing spoilage.^[40] In bread and dough fermentation, P. freudenreichii is incorporated into sourdough starters to enhance flavor through propionate production, which imparts a mild, nutty taste and extends shelf life by acting as a natural antimicrobial.^[41] Co-fermentation with lactic acid bacteria like Fructilactobacillus sanfranciscensis optimizes dough rheology and bread texture, reducing staling rates.^[42] Its potential extends to gluten-free ferments, where it improves sensory qualities in breads made from alternative flours, such as those from climate-resilient crops, by balancing acidity and boosting aroma without overpowering sourness.^[43] Experimental applications of P. freudenreichii in non-dairy ferments include vegetable and fruit-based lactic fermentations for bio-preservation, leveraging its propionate output to control pathogens in plant matrices.^[44] For instance, co-culturing with Lactobacillus plantarum enables growth in soymilk, producing stable fermented products with enhanced shelf life.^[44] In vegetable ferments like sauerkraut juice, it supports anaerobic conditions for propionic acid accumulation, inhibiting spoilage organisms during storage.^[45] Fruit-based trials remain limited but show promise for similar preservative effects in juices and purees. Recent studies (as of 2025) have explored its use in fermenting plant-based by-products, such as green pea canning waste, to produce vitamin B12-fortified foods, supporting sustainable nutrition in non-dairy matrices.^[46] Despite these benefits, challenges in adopting P. freudenreichii for broader fermented products stem from its slower growth rate compared to lactic acid bacteria, which delays fermentation onset and requires optimized co-cultures for industrial scalability.^[32] Its specific nutritional needs, such as amino acids, further limit standalone use in diverse matrices, necessitating strain selection and process adjustments.^[47]

Probiotic Applications

Health Benefits

Propionibacterium freudenreichii has demonstrated several health benefits as a probiotic, particularly in supporting gastrointestinal function. It promotes the growth of bifidobacteria in the human gut, acting as a bifidogenic agent that enhances beneficial microbiota composition.^[48] Clinical studies show that supplementation with P. freudenreichii, often in combination with other probiotics, alleviates symptoms of irritable bowel syndrome (IBS), including abdominal pain and bloating, by stabilizing the intestinal microbiota.^[49]^[50] Additionally, strains like CIRM-BIA 129 modulate gut microbiota diversity and reduce inflammation in models of colorectal issues.^[51] In terms of anti-inflammatory effects, P. freudenreichii mitigates symptoms in experimental colitis models, such as dextran sulfate sodium (DSS)-induced colitis in mice. Selected strains exhibit protective effects by lowering pro-inflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), in the colon.^[52]^[53] This immunomodulatory activity suggests potential for managing inflammatory bowel diseases (IBDs).^[54] Regarding cancer prevention, P. freudenreichii inhibits the growth of colon cancer cells through propionate-induced apoptosis. Studies from the early 2000s demonstrated that the bacterium triggers cell death in colorectal adenocarcinoma lines via acidic extracellular pH shifts and short-chain fatty acid production.^[55] Further research has explored its adjuvant role in therapies like TRAIL, enhancing apoptotic effects on cancer cells.^[56] Nutritionally, P. freudenreichii enhances vitamin B12 bioavailability, with bioaccessible forms produced during fermentation improving absorption in food products like wheat bran extracts.^[57] It also shows potential in allergy modulation; for instance, strain CIRM-BIA129 prevents food allergy development in mice by altering gut microbiota composition.^[58]

Mechanisms of Action

Propionibacterium freudenreichii exhibits probiotic mechanisms primarily through adhesion to host intestinal surfaces, immunomodulatory interactions, and metabolite-mediated effects on gut cells. Adhesion is facilitated by surface-layer proteins, notably SlpB, which enable binding to intestinal epithelial cells such as HT-29 human colon carcinoma cells. In adhesion assays, the wild-type strain CIRM-BIA 129 demonstrated significantly higher attachment rates (6.44 CFU per HT-29 cell) compared to the SlpB-deficient mutant, where adhesion was reduced to approximately 20% of wild-type levels.^[59] This protein's role extends to preserving mucosal integrity in vivo, as evidenced in mouse models of chemotherapy-induced mucositis, where SlpB contributes to reduced inflammation and maintained epithelial barrier function, implying interactions with mucus layers.^[60] Immunomodulation by P. freudenreichii involves the induction of regulatory T-cells (Tregs) and modulation of inflammatory pathways via short-chain fatty acids (SCFAs). The bacterium promotes an anti-inflammatory environment by increasing IL-10 production in intestinal epithelial cells and potentially enhancing Treg differentiation through its SCFA metabolites, such as propionate, which suppress pro-inflammatory cytokines like IL-17.^[60] Additionally, extracellular vesicles (EVs) derived from the strain CIRM-BIA 129 inhibit NF-κB activation in LPS-stimulated HT-29 cells in a dose-dependent manner, reducing pro-inflammatory responses; this effect is partially dependent on SlpB, as EVs from SlpB mutants show diminished potency.^[61] SCFAs produced by P. freudenreichii, including propionate and acetate, further contribute by activating G protein-coupled receptors and influencing NF-κB signaling to dampen innate immune activation. The metabolite propionate, a major fermentation product of P. freudenreichii, acts as a histone deacetylase (HDAC) inhibitor, altering gene expression in gut epithelial cells. In transcriptomic studies of HT-29 cells, exposure to P. freudenreichii or its SCFAs upregulated genes involved in NOD-like receptor signaling and mucin production (e.g., MUC2), promoting barrier integrity and reducing inflammation.^[27] Propionate's HDAC inhibition enhances apoptosis in colon cancer cells while sparing healthy epithelial cells, influencing epigenetic regulation of immune-related genes. Strain-specificity in these mechanisms arises from variations in surface-layer proteins, which determine anti-inflammatory potency. A multi-strain analysis revealed that SlpB and SlpE, characterized by S-layer homologous (SLH) domains, are present in strongly anti-inflammatory strains like CIRM-BIA 129 and CIRM-BIA 122, correlating with higher IL-10 induction in human peripheral blood mononuclear cells; these proteins were absent or varied in weakly or non-anti-inflammatory strains such as CIRM-BIA 118 and CIRM-BIA 121.^[62] In the strain ITG P20 (equivalent to CIRM-BIA 129), proteomic profiling identified 31 surface-exposed proteins, including SlpA, SlpB, SlpE, and InlA, whose combination underpins adhesion and immunomodulatory effects, absent in capsulated strains lacking these properties.^[63]

Biotechnology and Industrial Uses

Vitamin Production

Propionibacterium freudenreichii is a key microbial producer of vitamin B12 (cobalamin) through its anaerobic de novo biosynthesis pathway, which involves the formation of the corrin ring structure essential for the vitamin's core. This process occurs primarily under anaerobic conditions, where the bacterium assembles the corrin macrocycle from precursors like δ-aminolevulinic acid, followed by cobalt insertion to form cobinamide; however, microaeration is often required in later stages to facilitate attachment of the 5,6-dimethylbenzimidazole (DMBI) nucleotide loop for active cobalamin production.^[64]^[65] Industrial production of vitamin B12 by P. freudenreichii typically employs fed-batch fermentation strategies using cost-effective substrates such as glycerol or lactate, often derived from industrial wastes like biodiesel byproducts or dairy effluents. A common two-stage process involves initial anaerobic growth for biomass accumulation, followed by controlled microaeration to boost cobalamin yields, with optimizations including pH control, cobalt supplementation, and betaine addition to enhance metabolic flux. Yields in optimized fermenters can reach up to 47.6 mg/L using lactate-based media or higher, around 206 mg/L in advanced setups with expanded bed adsorption bioreactors and waste hydrolysates.^[64]^[66]^[67] Strains have been genetically engineered through genome shuffling, overexpression of biosynthetic genes like cob operons, or riboswitch modifications to increase production, achieving 2- to 3-fold improvements over wild-type levels.^[64]^[68] The vitamin B12 produced by P. freudenreichii finds applications as a nutritional supplement in fortified foods such as cereals, fermented dairy products, and plant-based alternatives, addressing deficiencies in vegan diets. Its Generally Recognized as Safe (GRAS) status by the FDA enables direct addition to these products without further processing, and it is also incorporated into animal feed formulations to enhance livestock nutrition and productivity.^[69]^[64]^[70] In addition to vitamin B12, P. freudenreichii generates folate (vitamin B9) and riboflavin (vitamin B2) as metabolic byproducts during fermentation, contributing to the overall nutritional profile of the biomass and enabling multi-vitamin enrichment in biotechnological outputs.^[64]^[71]^[72]

Bio-preservation

Propionibacterium freudenreichii plays a significant role in bio-preservation by producing antimicrobial metabolites, primarily propionic acid, during fermentation processes. This organic acid acts as a natural preservative by disrupting microbial cell membranes and inhibiting enzymatic activities in spoilage organisms. The efficacy of propionic acid is pH-dependent, with optimal inhibitory effects occurring at lower pH levels where the undissociated form predominates, enhancing its penetration into microbial cells.^[73]^[74] Propionic acid produced by P. freudenreichii effectively inhibits the growth of molds, such as Penicillium species, the pathogen Listeria monocytogenes, and various yeasts, including those responsible for food spoilage. This antimicrobial activity helps prevent fungal contamination and bacterial proliferation in food matrices, contributing to extended shelf life without relying on synthetic additives. Studies have demonstrated that propionic acid concentrations as low as 0.1-0.3% can significantly reduce mold and yeast counts in fermented products.^[75]^[76]^[74] In practical applications, P. freudenreichii cultures or their derived propionic acid are incorporated into bakery products like bread to combat mold growth, into processed meats to control Listeria and other pathogens, and into certain dairy items to inhibit yeast and bacterial spoilage. These uses allow for natural shelf-life extension, often reducing the need for chemical preservatives like sorbates or benzoates, thereby appealing to consumer preferences for clean-label foods. For instance, in bakery formulations, the addition of P. freudenreichii has been shown to delay visible mold appearance by up to several weeks under ambient storage conditions.^[77]^[78]^[79] Synergistic effects are observed when P. freudenreichii is combined with lactic acid bacteria, such as Lactiplantibacillus plantarum, which produce lactic acid and other metabolites that broaden the antimicrobial spectrum. This co-culture approach enhances inhibition of a wider range of fungi and bacteria, as the combined organic acids create a more hostile environment for spoilers while maintaining food safety and sensory qualities. Research on bread systems has highlighted such mixtures as effective biopreservatives, outperforming single cultures in antifungal performance.^[77]^[80] Regulatory approval supports the widespread use of P. freudenreichii and propionic acid in food preservation. In the United States, P. freudenreichii subsp. shermanii is affirmed as Generally Recognized as Safe (GRAS) for use as an antimicrobial agent in various foods, including at concentrations up to 0.3% propionic acid equivalent in bakery products. In the European Union, it holds Qualified Presumption of Safety (QPS) status, with propionic acid (E280) permitted as a preservative at levels such as 3 g/kg in bread, ensuring compliance with safety standards for direct addition to foods.^[69]^[1]^[81]

Genomics

Genome Structure

The first complete genome sequence of Propionibacterium freudenreichii was determined for the strain CIRM-BIA1 and published in 2010. This strain's genome consists of a single circular chromosome measuring 2,616,384 base pairs (bp) in length, with a G+C content of 67%. No plasmids were identified in this strain, though cryptic plasmids have been reported in 10–30% of P. freudenreichii isolates across various strains.^[28] The genome encodes 2,439 protein-coding genes, along with 2 ribosomal RNA operons and 45 transfer RNA genes, reflecting the bacterium's slow growth rate. Approximately 85% of the predicted proteins could be functionally annotated based on homology to known sequences. Key structural features include multiple insertion sequences (22 distinct families comprising 3.5% of the genome) and transposable elements, which contribute to genomic plasticity. The high G+C content aligns with the bacterium's placement within the Actinobacteria phylum.^[28] Notable gene clusters support core metabolic functions, such as propionate fermentation via the Wood-Werkman cycle; for instance, genes encoding methylmalonyl-CoA carboxytransferase (e.g., PFREUD_18840, PFREUD_18860, PFREUD_18870) are clustered, while a propionyl-CoA:succinate CoA transferase (PFREUD_00420) facilitates propionyl-CoA activation. Additionally, three CRISPR loci provide defense against bacteriophages: CRISPR1 (441,264–443,689 bp, 34 spacers), a smaller locus at 652,209–652,301 bp (1 spacer), and another at 2,215,874–2,216,038 bp (3 spacers), associated with cas genes for adaptive immunity.^[28]

Genetic Research

Comparative genomics studies of Propionibacterium freudenreichii have highlighted significant strain variation among dairy isolates, particularly in genes associated with probiotic functions such as surface proteins that mediate adhesion and host interaction. Sequencing of 20 complete genomes revealed that while core genes like S-layer protein SlpA are conserved across strains, SlpE is present in only a subset (e.g., 12 of 20 strains), often on genomic islands; accessory genomic elements, including pilus operons, vary considerably; for instance, strain JS18 possesses an intact pilus operon encoding a sortase (SrtC1) and fimbrial subunits, enabling specific mucus binding not observed in strains like JS or JS16.^[82] These differences, often localized to genomic islands, influence probiotic potential, with strains like CIRM-BIA1^T and CIRM-BIA 129 showing distinct surface protein profiles that affect anti-inflammatory and adhesion properties.^[63]^[28] Genetic engineering efforts have targeted enhancements in industrially relevant traits, including vitamin B₁₂ production and probiotic adhesion. Individual overexpression of biosynthetic genes such as cobA, cbiLF, or cbiEGH from the vitamin B₁₂ pathway increased yields 1.5- to 1.9-fold; a multigene approach involving hemA, hemB, and cobA in recombinant P. freudenreichii clones harboring expression vectors achieved 1.7 mg/L, representing a 2.2-fold improvement over controls.^[83] Genome-scale metabolic models have guided similar strategies, predicting and validating overexpression of the pentose phosphate pathway to boost propionate production fourfold during growth, with implications for B₁₂ pathway optimization by reducing competing fluxes.^[84] For probiotic applications, studies on surface layer proteins like SlpB demonstrate their role in adhesion to intestinal HT-29 cells, with strain-specific variations suggesting potential for targeted overexpression to enhance gut persistence, though direct engineering examples remain exploratory.^[85] Functional genomics, particularly transcriptomics, has elucidated adaptive responses during cheese ripening, revealing upregulation of acid tolerance mechanisms under cold and lactate stress. In strain CIRM-BIA1^T, microarray analysis during simulated ripening (30°C growth followed by 4°C) showed differential expression of 565 genes, including upregulation of lactate dehydrogenase (ldh2, fold change +1.9), alanine dehydrogenase (ald, +7.3), and L-serine dehydratase (sdaA, +3.5), which facilitate lactate conversion to pyruvate and mitigate acid accumulation.^[86] RNA-seq under nutritional shortage mimicking ripening further identified induction of chaperones like hsp20 (fold changes 6.7–6.9) and surface β-D-glucan synthesis genes (gtfF, +6.1), supporting long-term survival and acid stress tolerance through protein protection and metabolic rerouting.^[87] More recent genomic studies as of 2025 have expanded strain diversity insights. For example, the 2020 sequencing of strain T82 revealed 2,260 protein-coding genes and CRISPR loci contributing to genome stability. Transcriptomic analyses in 2024 elucidated aerobic adaptation in DSM 20271, highlighting metabolic shifts. A 2025 study identified single-nucleotide variants conditioning L-lactate catabolism inability in certain strains, with implications for cheese ripening efficiency.^[88]^[89]^[90] Looking ahead, synthetic biology approaches hold promise for P. freudenreichii improvement, including genome editing for novel metabolite production and phage resistance. Genome-scale models enable rational pathway rewiring, as demonstrated for propionate enhancement, paving the way for multiplexed edits via CRISPR/Cas systems to introduce synthetic operons for bioactive compounds.^[91] Complete genome sequences also reveal CRISPR arrays in strains like DSM 20271, suggesting potential for editing-based phage defense strategies, though applications remain nascent.^[6] These tools could expand P. freudenreichii's role beyond traditional uses, aligning with broader synthetic biology trends in food-grade bacteria.^[1]

References

[1]
The Complete Genome of Propionibacterium freudenreichii CIRM ...
Jul 23, 2010 · This species exhibits slow growth, low nutritional requirements, and hardiness in many habitats. It belongs to the taxonomic group of dairy propionibacteria.
[2]
https://www.sciencedirect.com/science/article/pii/B9780123744074000479
[3]
Identification of proteins involved in the anti-inflammatory properties ...
Apr 13, 2017 · Propionibacterium freudenreichii (Pf) is a food grade bacterium with GRAS (generally recognized as safe) status that belongs to the dairy ...
[4]
Propionibacterium freudenreichii (T) - SeqCode Registry
Oct 22, 2021 · P. freudenreichii is the type species of the genus Propionibacterium ... Taxonomy. Classification: Bacteria » Actinomycetota » Actinomycetes ...
[5]
Propionibacterium freudenreichii - an overview | ScienceDirect Topics
Propionibacterium freudenreichii is a commercially important microorganism that is used in the production of cheeses, cobalamin (vitamin B12), and propionic ...
[6]
Complete genome sequence of Propionibacterium freudenreichii ...
Oct 24, 2015 · P. freudenreichii is the type species of the genus Propionibacterium which contains Gram-positive, non-motile and non-sporeforming bacteria with ...Missing: taxonomic | Show results with:taxonomic
[7]
Propionibacterium freudenreichii subsp. shermanii (van Niel ... - ATCC
Propionibacterium freudenreichii subsp. shermanii (strain 9614) is a type strain, freeze-dried, stored at 2°C to 8°C, and is a bacteria.
[8]
Sequencing and Analysis of the Genome of Propionibacterium ...
Feb 24, 2020 · Propionic acid bacteria are divided into two groups based on the environment which they inhabit: skin (acnes) and classic (dairy). The former ...
[9]
Species: Propionibacterium freudenreichii - LPSN
⏰ According to Scholz and Kilian (2016), this species is an earlier heterotypic synonym of "Propionibacterium shermanii" van Niel 1928. Publication: Scholz CF, ...
[10]
The natural history of cutaneous propionibacteria, and ...
The natural history of cutaneous propionibacteria, and reclassification of selected species within the genus Propionibacterium to the proposed novel genera.
[11]
Genus: Propionibacterium - LPSN
Etymology: Pro.pi.o.ni.bac.te'ri.um. N.L. neut. n. acidum propionicum ... genus Propionibacterium to the proposed novel genera Acidipropionibacterium gen.
[12]
Alkane Nomenclature
In 1847 Dumas named the three-carbon acid PROPIONIC, from Greek proto (πρωτο, first) and pion (πιον, fat) again with the Lavoisier -ic suffix. The physical ...
[13]
Propionibacterium freudenreichii: General Characteristics and ...
Propionibacterium freudenreichii is a Gram-positive dairy probiotic bacterial species that has been used as a ripening starter in the production of Swiss-type ...
[14]
Permanent draft genome sequence of the probiotic strain ...
Jan 14, 2016 · P. freudenreichii CIRM-BIA129 (ITG P20) cells are Gram-positive, microaerophilic, pleiomorphic (coccoid to rod shape forming 'Chinese characters ...
[15]
Propionibacterium - Patrick - Major Reference Works
Sep 14, 2015 · Propionic acid fermentation of glycerol and glucose by Propionibacterium acidipropionici and Propionibacterium freudenreichii ... Von Freudenreich ...Missing: Edouard | Show results with:Edouard
[16]
The Complete Genome of Propionibacterium freudenreichii CIRM ...
P. freudenreichii is used in cheese ripening and as a probiotic, with a 2.6Mbp genome, 2439 protein-coding genes, and is hardy and slow-growing.
[17]
Propionibacterium freudenreichii Surface Protein SlpB Is Involved in ...
Jun 7, 2017 · Propionibacterium freudenreichii is a beneficial bacterium traditionally used as a cheese ripening starter and more recently for its probiotic ...
[18]
Propionibacterium freudenreichii thrives in microaerobic conditions ...
May 6, 2021 · Using an optimal microaerobic condition, P. freudenreichii DSM 20271 consumed lactate to produce propionate and acetate initially.
[19]
Use of Propionibacterium freudenreichii T82 Strain for Effective ...
Jun 29, 2021 · ... anaerobic. The optimal growth conditions for Propionibacterium are pH in the range of 6.0–7.0 and temperature in the range of 30–37 °C.
[20]
Microaerobic metabolism of lactate and propionate enhances ...
Oct 28, 2022 · In propionic acid bacteria B12 acts as a co-factor in the characteristic Wood-Werkman cycle used to ferment substrates such as lactate. B12 is ...
[21]
Interactions between Pyruvate and Lactate Metabolism in ... - PMC
In both types of experiments, acetate synthesis and the Wood-Werkman cycle were the metabolic pathways used most. Propionic acid bacteria, especially ...
[22]
[PDF] Improving the drying of Propionibacterium freudenreichii starter ...
Jun 11, 2021 · They were first described by Sigurd Orla-. Jensen and Eduard von Freudenreich at the beginning of the twentieth century (von Freudenreich and ...Missing: Edouard | Show results with:Edouard
[23]
Propionibacterium spp.—source of propionic acid, vitamin B12, and ...
Bacteria from the Propionibacterium genus were isolated and described in the first half of the twentieth century by Eduard von Freudenreich, Orl-Jensen, and ...Missing: etymology | Show results with:etymology
[24]
The Propionic Acid Bacteria - ASM Journals
Propionibacterium Freudenreichii van Niel 1928. Synonym. Bacterium acidi-propionici a von Freudenreich and. Orla-Jensen 1906. Cultures. 1 and 2. Morphology.
[25]
https://pmc.ncbi.nlm.nih.gov/articles/PMC5756557/
[26]
https://journals.asm.org/doi/pdf/10.1128/jb.26.4.393-417.1933
[27]
Fine-Tuning of Process Parameters Modulates Specific Metabolic ...
Jul 20, 2021 · An appropriate culture volume, corresponding to a final population of 6 × 106 cfu per mL in the milk used for cheese making, was centrifuged for ...
[28]
Adaptation of Propionibacterium freudenreichii to long-term survival ...
Dec 8, 2016 · Propionibacterium freudenreichii is an Actinobacterium widely used in the dairy industry and responsible for aroma development and opening (eyes) ...Missing: timeline | Show results with:timeline
[29]
Propionic acid bacteria in the food industry: An update on essential ...
Aug 6, 2021 · freudenreichii is prototrophic for all amino acids and nucleotides, whereas concerning vitamins, some PAB strains require only pantothenate and ...
[30]
Cheeses with Propionic Acid Fermentation - ScienceDirect.com
Propionic acid fermentation leads to characteristic eyes and a nutty-sweetish cheese flavor; usually achieved by a culture of propionic acid bacteria (PAB).
[31]
Influence of processing and ripening parameters on starter, non ...
No growth of P. freudenreichii was reported at 2.8°C. Most cheeses with a PAB fermentation undergo a hot room ripening step (20–24°C) (Fröhlich- ...
[32]
A Temporal -omic Study of Propionibacterium freudenreichii CIRM ...
Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. It grows when cheeses are ripened in a warm room (about 24°C).
[33]
Antifungal effect of dairy propionibacteria--contribution of organic acids
Propionic acid, followed by acetic acid, was the most potent antifungal acid. Inhibition at pH 7 generally required concentrations above 500 mM for all three ...
[34]
Propionibacterium freudenreichii strains quantitatively affect ...
Aug 6, 2025 · Volatile compounds produced in Swiss cheese by Propionibacterium freudenreichii, one of the species essential for the development of the ...
[35]
Silage review: Recent advances and future uses of silage additives
pentosaceus and Propionibacterium freudenreichii performed similarly. These results indicate that a combination inoculant is capable of dominating the early ...
[36]
[PDF] Propionibacteria and their role in the biological control of aerobic ...
May 11, 2020 · Propionic acid can be formed in silage by several micro-organisms other than propi- onibacteria, including Micrococcus lacti- lyticus, ...
[37]
USE OF Lactobacillus plantarum AND Propionibacterium ...
Bacterial inoculant as feed additives have been shown to be beneficial in silage fermentation in many parts of the world. However, there is still not much ...
[38]
Effects and mechanisms for enhancing bread quality and extending ...
Incorporating Propionibacterium freudenreichii (PAB) into sourdough presents a promising solution, as compared to lactic acid produced primarily by LAB ...
[39]
Production of wheat bread without preservatives using sourdough ...
The starter sourdoughs that include Propionibacterium freudenreichii ssp. shermanii NBIMCC 327 had greater antimicrobial activity against saprophytic ...
[40]
Ingredients from Climate Resilient Crops to Enhance the Nutritional ...
May 31, 2022 · Propionibacterium freudenreichii also has the potential to enhance the sensory quality of gluten-free ... fermentation with Propionibacterium ...
[41]
Differential Adaptation of Propionibacterium freudenreichii CIRM ...
Dec 1, 2020 · As shown in Figure 1, P. freudenreichii grew in UHT cow's milk to reach a final population of 6 × 108 CFU.mL–1. Interestingly, this growth ...
[42]
https://www.tandfonline.com/doi/full/10.1080/13102818.2014.965057
[43]
Inability of dairy propionibacteria to grow in milk from low inocula
Aug 6, 2025 · Because of its nitrogen requirements, P. freudenreichii is known to grow poorly in milk (Falentin et al., 2010; Piveteau et al., 2000) , thus ...
[44]
Growth Stimulator for Bifidobacteria Produced by Propionibacterium ...
Growth Stimulator for Bifidobacteria Produced by Propionibacterium Freudenreichii and Several Intestinal Bacteria. J Dairy Sci. 1994 Feb;77(2):393-404. doi ...
[45]
A probiotic mixture alleviates symptoms in irritable bowel syndrome ...
rhamnosus LC705, Bifidobacterium breve Bb99 and Propionibacterium freudenreichii ssp. shermanii JS is effective in alleviating irritable bowel syndrome symptoms ...Missing: "gastrointestinal | Show results with:"gastrointestinal
[46]
Clinical trial: multispecies probiotic supplementation alleviates the ...
Jan 1, 2008 · rhamnosus Lc705, Propionibacterium freudenreichii ssp. shermanii JS and Bifidobacterium animalis ssp. lactis Bb12) on abdominal symptoms ...Missing: "gastrointestinal | Show results with:"gastrointestinal<|separator|>
[47]
Propionibacterium freudenreichii CIRM-BIA 129 Osmoadaptation ...
Oct 9, 2019 · Propionibacterium freudenreichii is a beneficial bacterium with documented effects on the gut microbiota and on inflammation.
[48]
Propionibacterium freudenreichii CIRM-BIA 129 mitigates colitis ...
Feb 1, 2024 · Propionibacterium freudenreichii CIRM-BIA 129 mitigates colitis through S layer protein B-dependent epithelial strengthening · Abstract.
[49]
Propionibacterium freudenreichii component 1.4-dihydroxy-2 ...
Propionibacterium freudenreichii component 1.4-dihydroxy-2-naphthoic acid ... IL-6, and TNF-alpha in DSS treated colon. In addition, the decreased ...
[50]
Dairy Propionibacteria: Probiotic Properties and Their Molecular ...
Jun 17, 2025 · P. freudenreichii strains have been shown to mitigate inflammatory bowel diseases (IBDs) and mucositis and prevent necrotizing enterocolitis ( ...Missing: benefits | Show results with:benefits
[51]
Acidic extracellular pH shifts colorectal cancer cell death ... - PubMed
The human probiotic Propionibacterium freudenreichii kills colorectal adenocarcinoma cells through apoptosis ... colon cancer cells. Publication types.
[52]
The probiotic Propionibacterium freudenreichii as a new ... - PubMed
Feb 9, 2016 · TRAIL is pro-apoptotic on colon cancer cells ... Keywords: Propionibacterium freudenreichii; RNA microarrays; SCFA; TRAIL; colon cancer.
[53]
Bioaccessibility of vitamin B12 synthesized by Propionibacterium ...
Jul 27, 2021 · Bioaccessibility of vitamin B12 synthesized by Propionibacterium freudenreichii and from products made with fermented wheat bran extract.
[54]
Propionibacterium freudenreichii Prevents Food Allergy in Mice via ...
Dec 11, 2024 · In this context, we investigated the potential impact of Propionibacterium freudenreichii CIRM-BIA129, a recognized immunomodulatory probiotic ...
[55]
https://pubmed.ncbi.nlm.nih.gov/17195096/
[56]
https://pubmed.ncbi.nlm.nih.gov/26771233/
[57]
https://pubmed.ncbi.nlm.nih.gov/34382008/
[58]
https://pubmed.ncbi.nlm.nih.gov/39576212/
[59]
https://doi.org/10.3389/fmicb.2017.01033
[60]
Fermentative production of vitamin B12 by Propionibacterium ... - NIH
The prime objective of this study is to clarify the metabolic pathway's effective synthesis of vitamin B12 via controlled fermentation. This study aims to ...
[61]
Oxygen determines the requirement for cobalamin but not riboflavin ...
Jul 29, 2025 · freudenreichii strains were routinely cultured in yeast extract sodium lactate (YEL) medium, a standard medium for propionibacteria. This medium ...
[62]
Vitamin B12 production from crude glycerol by Propionibacterium ...
A two-step statistical experimental design was employed to optimize the medium for vitamin B12 production from crude glycerol by Propionibacterium ...
[63]
Microaerobic metabolism of lactate and propionate enhances ...
Oct 28, 2022 · Here we show biomass formation increases 2.7 times for P. freudenreichii grown in microaerobic conditions on lactate versus anaerobic conditions.
[64]
Production of vitamin B12 in genetically engineered ...
We successfully achieved the production of about 1.7 mg/l vitamin B 12 , 2.2-fold higher than that produced by P. freudenreichii harboring pPK705.
[65]
GRN No. 128 - GRAS Notices - FDA
Skim milk or dextrose cultured with Propionibacterium freudenreichii subsp. shermanii. Intended Use: Use as an antimicrobial agent in cheeses, sauces, salad ...
[66]
Food-Like Growth Conditions Support Production of Active Vitamin ...
The analyses of growth kinetics of P. freudenreichii 2067 in PPA and WBM media revealed notable differences including a 1.5-h shorter generation time in PPA ...
[67]
Optimisation of vitamin B 12 and folate production by ...
The aim of this study was to evaluate different regimes for inclusion of a vitamin B 12 and folate producing Propionibacterium strain into kefir grains.
[68]
Production of Vitamin B2 (Riboflavin) by Microorganisms: An Overview
... Propionibacterium freudenreichii ssp. shermanii as starter cultures significantly increased the riboflavin content of milk (Le Blanc et al., 2011). Burgess ...
[69]
Growth, Inhibition, and Survival of Listeria monocytogenes ... - PubMed
In the pH range tested, this inhibitory pH was 5.0 for propionic acid, 4.5 for acetic and lactic acids, and 4.0 for citric and hydrochloric acids. All four ...<|control11|><|separator|>
[70]
Propionic Acid Fermentation—Study of Substrates, Strains ... - MDPI
The study compares valorization of lactose and lactates—the main carbon sources of whey—by fermentation—an environmentally friendly process ...
[71]
Propionibacteria as promising tools for the production of ... - Frontiers
Strains of P. freudenreichii and A. acidipropionici (formerly Propionibacterium acidipropionici) are commonly utilized in dairy industry as starters for Swiss ...
[72]
Inhibition of Listeria monocytogenes by propionic acid-based ...
The objective of this study was to determine the inhibition of L. monocytogenes by propionic acid-based ingredients in high-moisture, cured turkey stored at 4 ...
[73]
A mixed culture of Propionibacterium freudenreichii and ...
This is the first study demonstrating the mixed culture of Propionibacterium freudenreichii and Lactobacillus as viable antifungal agent in bread system.
[74]
US10334862B2 - Methods for preserving processed meats
One illustrative example of such a bacterium is Propionibacterium freudenreichii. The exogenous enzymes may include enzymes that convert glycogen to lactate. In ...
[75]
US5260061A - Propionibacteria metabolites inhibit spoilage yeast in ...
In bread, which is a high solids food, propionic acid or its salts are a preferred preservative in concentrations of 0.2% to 0.38% of the flour content to ...
[76]
Co-fermentation of Propionibacterium freudenreichii and ... - NIH
Jul 5, 2019 · The present study investigated the effect of co-fermentation on vitamin B12 content and microbiological composition of wheat bran.
[77]
What is Propionic Acid (E280) in Food and its Uses? - foodadditives
Apr 9, 2020 · Is Propionic Acid Safe to Eat? Yes, it has been approved as a safe ingredient by the U.S. Food and Drug Administration (FDA) and the European ...
[78]
De novo assembly of genomes from long sequence reads reveals ...
Propionibacterium freudenreichii is an industrially important bacterium granted the Generally Recognized as Safe (the GRAS) status, due to its long safe use ...Missing: pct | Show results with:pct
[79]
Production of vitamin B12 in genetically engineered ... - PubMed
... vitamin B12 in Propionibacterium freudenreichii, which is a known producer of vitamin B12. ... mg/l vitamin B12, 2.2-fold higher than that produced by P ...
[80]
Genome-scale model guided design of Propionibacterium for ...
The combination of this pathway with glycolysis and the Wood-Werkman cycle enables the production of 1.6 mol propionate/mol glucose and 0.8 moles of formate ...
[81]
Propionibacterium freudenreichii Surface Protein SlpB Is Involved in ...
Jun 8, 2017 · Propionibacterium freudenreichii is a GRAS (Generally Recognized As Safe) actinobacterium consumed in high amounts in fermented dairy products.
[82]
A Temporal -omic Study of Propionibacterium freudenreichii CIRM ...
Jan 13, 2012 · Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. It grows when cheeses are ripened in a warm room ...Missing: adoption early
[83]
Adaptation of Propionibacterium freudenreichii to long-term survival ...
Dec 8, 2016 · Propionibacterium freudenreichii is an Actinobacterium widely used in the dairy industry and responsible for aroma development and opening (eyes) ...
[84]
Genome-scale model guided design of Propionibacterium for ...
Nov 24, 2017 · The recent generation of genome-scale models for a number of Propionibacterium species facilitates the rational design of metabolic engineering ...