Improved propionic acid and 5,6-dimethylbenzimidazole control strategy for vitamin B12 fermentation by Propionibacterium freudenreichii

Co-culturing Propionibacterium freudenreichii and Bifidobacterium animalis subsp. lactis improves short-chain fatty acids and vitamin B12 contents in soy whey

The lack of vitamin B12 in unprocessed plant-based foods can lead to health problems in strict vegetarians and vegans. The main aim of this study was to investigate the potential synergy of co-culturing Bifidobacterium animalis subsp. lactis and Propionibacterium freudenreichii in improving production of vitamin B12 and short-chain fatty acids in soy whey. Different strategies including mono-, sequential and simultaneous cultures were adopted. Growth, short-chain fatty acids and vitamin B12 were assessed throughout the fermentation while free amino acids, volatiles, and isoflavones were determined on the final day. P. freudenreichii monoculture grew well in soy whey, whereas B. lactis monoculture entered the death phase by day 4. Principal component analysis demonstrates that metabolic changes in both sequential cultures did not show drastic differences to those of P. freudenreichii monoculture. However, simultaneous culturing significantly improved vitamin B12, acetic acid and propionic acid contents (1.3 times, 5 times, 2.5 times, compared to the next highest treatment [sequential cultures]) in fermented soy whey relative to other culturing modes. Hence, co-culturing of P. freudenreichii and B. lactis would provide an alternative method to improve vitamin B12, acetic acid and propionic acid contents in fermented foods.

Gut health benefits and associated systemic effects provided by functional components from the fermentation of natural matrices

Recently, the role of the gut microbiota in metabolic health, immunity, behavioral balance, longevity, and intestine comfort has been the object of several studies from scientific communities. They were encouraged by a growing interest from food industries and consumers toward novel fermented ingredients and formulations with powerful biological effects, such as pre, pro, and postbiotic products. Depending on the selected strains, the operating conditions, the addition of suitable reagents or enzymes, the equipment, and the reactor configurations, functional compounds with high bioactivity, such as short-chain fatty acids, gamma-aminobutyric acid, bioactive peptides, and serotonin, can be enhanced and/or produced through fermentation of several vegetable matrices. Otherwise, their formation can also be promoted directly in the gut after the dietary intake of fermented foods: In this case, fermentation will aim to increase the content of precursor substances, such as indigestible fibers, polyphenols, some amino acids, and resistant starch, which can be potentially metabolized by endogenous gut microorganisms and converted in healthy molecules. This review provides an overview of the main functional components currently investigated in literature and the associated gut health benefits. The current state of the art about fermentation technology as a promising functionalization tool to promote the direct or indirect formation of gut-health-enhancing components was deepened, highlighting the importance of optimizing microorganism selection, system setups, and process conditions according to the target compound of interest. The collected data suggested the possibility of gaining novel functional food ingredients or products rich in functional molecules through fermentation without performing additional extraction and purification stages, which are needed when conventional culture broths are used.

Research on the targeted improvement of the yield of a new VB12-producing strain, Ensifer adhaerens S305, based on genomic and transcriptomic analysis

BACKGROUND

Vitamin B12 (VB12) has a wide range of applications and high economic value. In this study, a new strain with high VB12 production potential, Ensifer adhaerens S305, was identified in sewage. Because E. adhaerens strains have become the main strains for VB12 production via fermentation in recent years, the directional modification of the S305 strain to obtain a strain suitable for the industrial production of VB12 has great potential and commercial value.

RESULTS

16S rRNA and genome-wide phylogenetic tree analysis combined with average nucleotide identity (ANI) analysis showed that the high-yielding VB12 strain was a E. adhaerens strain and that its VB12 synthesis pathway genes were highly similar to related genes of strains of this and other species, including E. adhaerens Casida A, Pseudomonas denitrificans SC 510, and E. adhaerens Corn53. High-pressure liquid chromatography (HPLC) results indicated that the VB12 yields of the S305 strain were more than double those of the Casida A strain under different medium components. Multiple genes with significantly upregulated and downregulated transcription were identified by comparing the transcription intensity of different genes through transcriptome sequencing. KEGG enrichment analysis of the porphyrin metabolism pathway identified 9 significantly upregulated and downregulated differentially expressed genes (DEGs) in the VB12 synthesis pathway, including 7 transcriptionally upregulated genes (cobA, cobT, hemA, cobJ, cobN, cobR, and cobP) that were episomally overexpressed in the Casida A strain. The results showed that the VB12 yield of the overexpressed strain was higher than that of the wild-type strain. Notably, the strains overexpressing the cobA and cobT genes exhibited the most significant increases in VB12 yield, i.e., 31.4% and 24.8%, respectively. The VB12 yield of the S305 strain in shake-flask culture was improved from 176.6 ± 8.21 mg/L to 245.6 ± 4.36 mg/L by integrating the cobA and cobT genes into the strain.

CONCLUSION

Phylogenetic tree and ANI analysis showed that the Ensifer and Sinorhizobium strains were quite different at the genome level; the overexpression and integrated expression of significantly upregulated genes in the VB12 synthesis pathway could increase the yield of VB12, further improving the VB12 yield of the E. adhaerens S305 strain.

Effect of blocking the haem synthesis pathway and weakening the haem synthesis pathway for sirohaem on the growth of and vitamin B12 synthesis in Ensifer adhaerens Casida A

To block and weaken the bacterial branched VB12 synthetic metabolic pathway, homologous recombination technology was used to knock out the sirohaem synthase gene cysG located in the chromosome and the endogenous A plasmid of the Ensifer adhaerens Casida A strain, and the expression of the uroporphyrinogen III decarboxylase gene hemE was weakened by weak promoter substitution. The growth of the engineered strains and the production of VB12 and haem were analysed and measured in the engineered strains, aiming to provide a new strategy for enhancement of VB12 biosynthesis. The results showed that the chromosomal cysG gene knockout strain ΔcysG, endogenous A plasmid cysG gene knockout strain ΔpAcysG and cysG gene double knockout strain ΔcysGΔpAcysG grew normally, with VB12 yield increases of 19.9%, 11.2%, and 27.4% compared to the starting strain, respectively. In the background of the cysG gene knockout strain, the expression of the hemE gene was weakened, resulting in the generation of the strain ΔcysGΔpAcysG-E-pdnaD, and the VB12 yield of ΔcysGΔpA cysG-E-pdnaD reached 114.17 ± 5.77 mg L-1, an increase of 45.1% compared to the yield of the original strain. The above results indicate that the strategy of increasing VB12 production by knocking out the haem synthesis pathway and weakening the haem synthesis pathway is effective.

A synthetic cell-free 36-enzyme reaction system for vitamin B12 production

Adenosylcobalamin (AdoCbl), a biologically active form of vitamin B12 (coenzyme B12), is one of the most complex metal-containing natural compounds and an essential vitamin for animals. However, AdoCbl can only be de novo synthesized by prokaryotes, and its industrial manufacturing to date was limited to bacterial fermentation. Here, we report a method for the synthesis of AdoCbl based on a cell-free reaction system performing a cascade of catalytic reactions from 5-aminolevulinic acid (5-ALA), an inexpensive compound. More than 30 biocatalytic reactions are integrated and optimized to achieve the complete cell-free synthesis of AdoCbl, after overcoming feedback inhibition, the complicated detection, instability of intermediate products, as well as imbalance and competition of cofactors. In the end, this cell-free system produces 417.41 μg/L and 5.78 mg/L of AdoCbl using 5-ALA and the purified intermediate product hydrogenobyrate as substrates, respectively. The strategies of coordinating synthetic modules of complex cell-free system describe here will be generally useful for developing cell-free platforms to produce complex natural compounds with long and complicated biosynthetic pathways.

Developing a single-stage continuous process strategy for vitamin B12 production with Propionibacterium freudenreichii

BACKGROUND

Vitamin B₁₂ is a widely used compound in the feed and food, healthcare and medical industries that can only be produced by fermentation because of the complexity of its chemical synthesis. Besides, the use of Generally Recognized as Safe (GRAS) and Qualified Presumption of Safety (QPS) microorganisms, like Propionibacterium freudenreichii, especially non-GMO wild-type producers, are becoming an interesting alternative in markets where many final consumers have high health and ecological awareness. In this study, the production of vitamin B₁₂ using the Propionibacterium freudenreichii NBRC 12391 wild-type strain was characterized and optimized in shake flasks before assessing several scale-up strategies.

RESULTS

Initial results established that: (i) agitation during the early stages of the culture had an inhibitory effect on the volumetric production, (ii) 5,6-dimethylbenzimidazole (DMBI) addition was necessary for vitamin B₁₂ production, and (iii) kinetics of vitamin B₁₂ accumulation were dependent on the induction time when DMBI was added. When scaling up in a bioreactor, both batch and fed-batch bioprocesses proved unsuitable for obtaining high volumetric productivities mainly due to carbon source limitation and propionic acid inhibition, respectively. To overcome these drawbacks, an anaerobic single-phase continuous bioprocess strategy was developed. This culture strategy was maintained stable during more than 5 residence times in two independent cultures, resulting in 5.7-fold increase in terms of volumetric productivity compared to other scale-up strategies.

CONCLUSION

Overall, compared to previously reported strategies aimed to reduce propionic acid inhibition, a less complex anaerobic single-phase continuous and more scalable bioprocess was achieved.

Microaerobic metabolism of lactate and propionate enhances vitamin B12 production in Propionibacterium freudenreichii

BACKGROUND

Propionibacterium freudenreichii is used in biotechnological applications to produce vitamin B₁₂. Although cultured mainly in anaerobic conditions, microaerobic conditions can greatly enhance biomass formation in P. freudenreichii. Since B₁₂ yields may be coupled to biomass formation, microaerobic conditions show great potential for increasing B₁₂ yields in P. freudenreichii.

RESULTS

Here we show biomass formation increases 2.7 times for P. freudenreichii grown in microaerobic conditions on lactate versus anaerobic conditions (1.87 g/L vs 0.70 g/L). Consumption of lactate in microaerobic conditions resulted first in production of pyruvate, propionate and acetate. When lactate was depleted, pyruvate and propionate were oxidised with a concomitant sixfold increase in the B₁₂ titer compared to anaerobic conditions, showing potential for propionate and pyruvate as carbon sources for B₁₂ production. Consequently, a fed-batch reactor with anaerobically precultured lactate-grown cells was fed propionate in microaerobic conditions resulting in biomass increase and production of B₁₂. Vitamin yields increased from 0.3 [Formula: see text] B₁₂ per mmol lactate in anaerobic conditions to 2.4 [Formula: see text] B₁₂ per mmol lactate and 8.4 [Formula: see text] B₁₂ per mmol propionate in microaerobic conditions. Yield per cell dry weight (CDW) increased from 41 [Formula: see text] per g CDW in anaerobic conditions on lactate to 92 [Formula: see text] per g CDW on lactate and 184 [Formula: see text] per g CDW on propionate in microaerobic conditions.

CONCLUSIONS

Here we have shown both B₁₂ yield per substrate and per CDW were highest on cells oxidising propionate in microaerobic conditions, showing the potential of propionate for biotechnological production of vitamin B₁₂ by P. freudenreichii.

Bioprocess Strategies for Vitamin B12 Production by Microbial Fermentation and Its Market Applications

Vitamin B₁₂ is a widely used compound in the feed and food, healthcare and medical industries that can only be produced by fermentation because of the complexity of its chemical synthesis. For this reason, finding better producer strains and optimizing their bioprocesses have been the main focus of industrial producers over the last few decades. In this review, we initially provide a historical overview of vitamin B₁₂ research and the main biosynthetic characteristics of the two microorganism families typically used for its industrial production: several strains of Propionibacterium freudenreichii and strains related to Pseudomonas denitrificans. Later, a complete summary of the current state of vitamin B₁₂ industrial production as well as the main advances and challenges for improving it is detailed, with a special focus on bioprocess optimization, which aims not only to increase production but also sustainability. In addition, a comprehensive list of the most important and relevant patents for the present industrial strains is provided. Finally, the potential applications of vitamin B₁₂ in different markets are discussed.

High Cell Density Culture of Dairy Propionibacterium sp. and Acidipropionibacterium sp.: A Review for Food Industry Applications

The dairy bacteria Propionibacterium sp. and Acidipropionibacterium sp. are versatile and potentially probiotic microorganisms showing outstanding functionalities for the food industry, such as the production of propionic acid and vitamin B₁₂ biosynthesis. They are the only food grade microorganisms able to produce vitamin B₁₂. However, the fermentation batch process using these bacteria present some bioprocess limitations due to strong end-product inhibition, cells slow-growing rates, low product titer, yields and productivities, which reduces the bioprocess prospects for industrial applications. The high cell density culture (HCDC) bioprocess system is known as an efficient approach to overcome most of those problems. The main techniques applied to achieve HCDC of dairy Propionibacterium are the fed-batch cultivation, cell recycling, perfusion, extractive fermentation, and immobilization. In this review, the techniques available and reported to achieve HCDC of Propionibacterium sp. and Acidipropionibacterium sp. are discussed, and the advantages and drawbacks of this system of cultivation in relation to biomass formation, vitamin B₁₂ biosynthesis, and propionic acid production are evaluated.

Recent advances in microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway

Tetrapyrroles are essential metabolic components produced by almost all organisms, and they participate in various fundamental biological processes. Tetrapyrroles are used as pharmaceuticals, food additives, and nutraceuticals, as well as in agricultural applications. However, their production is limited by their low extraction yields from natural resources and by the complex reaction steps involved in their chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, microbial cell factories were developed as an alternative method for tetrapyrrole production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway (e.g., 5-aminolevulinic acid, heme, bilins, chlorophyll, and vitamin B₁₂). Furthermore, outstanding challenges to the microbial production of tetrapyrrole compounds, as well as their possible solutions, are discussed.

Metabolic profiling analysis of the vitamin B12 producer Propionibacterium freudenreichii

Vitamin B₁₂ (VB₁₂) is an indispensable cofactor of metabolic enzymes and has been widely used in the food and pharmaceutical industries. In this study, the effects of medium composition on VB₁₂ production by Propionibacterium freudenreichii were evaluated and optimized based on statistical experiments. The results showed that glucose, yeast extract, KH₂PO₄, and glycine have significant effects on VB₁₂ production. The final titer of VB₁₂ reached 8.32 ± 0.02 mg/L, representing a 120% increase over the non‐optimized culture medium. We employed a metabolomics approach to analyze the differences of metabolite concentrations in P. freudenreichii cells cultivated in the original medium and optimized fermentation medium. Using multivariate data analysis, we identified a range of correlated metabolites, illustrating how metabolomics can be used to explain VB₁₂ production changes by corresponding differences in the overall cellular metabolism. The concentrations of many metabolic intermediates of glycolysis, the Wood–Werkman cycle, the TCA cycle, and amino acid metabolism were increased, which contributed to the synthesis of propionic acid and VB₁₂ due to an improved supply of energy and precursors.

Microbial and Genetic Resources for Cobalamin (Vitamin B12) Biosynthesis: From Ecosystems to Industrial Biotechnology

Many microbial producers of coenzyme B12 family cofactors together with their metabolically interdependent pathways are comprehensively studied and successfully used both in natural ecosystems dominated by auxotrophs, including bacteria and mammals, and in the safe industrial production of vitamin B12. Metabolic reconstruction for genomic and metagenomic data and functional genomics continue to mine the microbial and genetic resources for biosynthesis of the vital vitamin B12. Availability of metabolic engineering techniques and usage of affordable and renewable sources allowed improving bioprocess of vitamins, providing a positive impact on both economics and environment. The commercial production of vitamin B12 is mainly achieved through the use of the two major industrial strains, Propionobacterium shermanii and Pseudomonas denitrificans, that involves about 30 enzymatic steps in the biosynthesis of cobalamin and completely replaces chemical synthesis. However, there are still unresolved issues in cobalamin biosynthesis that need to be elucidated for future bioprocess improvements. In the present work, we review the current state of development and challenges for cobalamin (vitamin B12) biosynthesis, describing the major and novel prospective strains, and the studies of environmental factors and genetic tools effecting on the fermentation process are reported.

Propionic acid production by Propionibacterium freudenreichii using sweet sorghum bagasse hydrolysate

Propionic acid, a widely used food preservative and intermediate in the manufacture of various chemicals, is currently produced from petroleum-based chemicals, raising concerns about its long-term sustainability. A key way to make propionic acid more sustainable is through fermentation of low-cost renewable and inedible sugar sources, such as lignocellulosic biomass. To this end, we utilized the cellulosic hydrolysate of sweet sorghum bagasse (SSB), a residue from a promising biomass source that can be cultivated around the world, for fermentative propionic acid production using Propionibacterium freudenreichii. In serum bottles, SSB hydrolysate supported a higher propionic acid yield than glucose (0.51 vs. 0.44 g/g, respectively), which can be attributed to the presence of additional nutrients in the hydrolysate enhancing propionic acid biosynthesis and the pH buffering capacity of the hydrolysate. Additionally, SSB hydrolysate supported better cell growth kinetics and higher tolerance to product inhibition by P. freudenreichii. The yield was further improved by co-fermenting glycerol, a renewable byproduct of the biodiesel industry, reaching up to 0.59 g/g, whereas volumetric productivity was enhanced by running the fermentation with high cell density inoculum. In the bioreactor, although the yield was slightly lower than in serum bottles (0.45 g/g), higher final concentration and overall productivity of propionic acid were achieved. Compared to glucose (this study) and hydrolysates from other biomass species (literature), use of SSB hydrolysate as a renewable glucose source resulted in comparable or even higher propionic acid yields. KEY POINTS: • Propionic acid yield and cell growth were higher in SSB hydrolysate than glucose. • The yield was enhanced by co-fermenting SSB hydrolysate and glycerol. • The productivity was enhanced under high cell density fermentation conditions. • SSB hydrolysate is equivalent or superior to other reported hydrolysates.

Propionic Acid: Method of Production, Current State and Perspectives

During the past years, there has been a growing interest in the bioproduction of propionic acid by Propionibacterium. One of the major limitations of the existing models lies in their low productivity yield. Hence, many strategies have been proposed in order to circumvent this obstacle. This article provides a comprehensive synthesis and review of important biotechnological aspects of propionic acid production as a common ingredient in food and biotechnology industries. We first discuss some of the most important production processes, mainly focusing on biological production. Then, we provide a summary of important propionic acid producers, including Propionibacterium freudenreichii and Propionibacterium acidipropionici, as well as a wide range of reported growth/production media. Furthermore, we describe bioprocess variables that can have impact on the production yield. Finally, we propose methods for the extraction and analysis of propionic acid and put forward strategies for overcoming the limitations of competitive microbial production from the economical point of view. Several factors influence the propionic acid concentration and productivity such as culture conditions, type and bioreactor scale; however, the pH value and temperature are the most important ones. Given that there are many reports about propionic acid production from glucose, whey permeate, glycerol, lactic acid, hemicelluloses, hydrolyzed corn meal, lactose, sugarcane molasses and enzymatically hydrolyzed whole wheat flour, only few review articles evaluate biotechnological aspects, i.e. bioprocess variables.

Metabolic engineering and optimization of the fermentation medium for vitamin B12 production in Escherichia coli

Vitamin B₁₂ is a crucial fine chemical that is widely used in the pharmaceutical, food and chemical industries, and its production solely dependents on microbial fermentation. We previously constructed an artificial vitamin B₁₂ biosynthesis pathway in Escherichia coli, but the yield of the engineered strains was low. Here, we removed metabolic bottlenecks of the vitamin B₁₂ biosynthesis pathway in engineered E. coli strains. After screening cobB genes from different sources, optimizing the expression of cobN and customizing the ribosome binding sites of cobS and cobT, the vitamin B₁₂ yield increased to 152.29 μg/g dry cell weight (DCW). Optimization of the downstream module, which converts co(II)byrinic acid a,c-diamide into adenosylcobinamide phosphate, elevated the vitamin B₁₂ yield to 249.04 μg/g DCW. A comparison of a variety of equivalent components indicated that glucose and corn steep liquor are optimal carbon and nitrogen sources, respectively. Finally, an orthogonal array design was applied to determine the optimal concentrations of glucose and nitrogen sources including corn steep liquor and yeast extract, through which a vitamin B₁₂ yield of 530.29 μg/g DCW was obtained. The metabolic modifications and optimization of fermentation conditions achieved in this study offer a basis for further improving vitamin B₁₂ production in E. coli and will hopefully accelerate its industrial application.

Biosynthesis of vitamin B12 by Propionibacterium freudenreichii subsp. shermanii ATCC 13673 using liquid acid protein residue of soybean as culture medium

Vitamin B12 deficiency still persists, mainly caused by low intake of animal food products affecting vegetarians, vegans, and populations of underdeveloped countries. In this study, we investigate the biosynthesis of vitamin B12 by potential probiotic bacterium using an agroindustry residue, the liquid acid protein residue of soybean (LAPRS), as a low-cost, animal derivate-free alternative culture medium. Cultures of Propionibacterium freudenreichii subsp. shermanii ATCC 13673 growing in LAPRS for vitamin B12 biosynthesis were studied using the Plackett-Burman experimental approach, followed by a central composite design 2² to optimize the concentration of significant variables. We also performed a proteolytic treatment of LAPRS and evaluated the optimized-hydrolyzed medium influence on the microbial growth and metabolism in shaker flask and bioreactor experiments. In this all-plant source medium, P. freudenreichii subsp. shermanii produced high concentrations of cells and high amounts of vitamin B12 (0.6 mg/g cells) after process optimization. These results suggest the possibility of producing vitamin B12 by a potential probiotic bacterium in a very cheap, animal derivate-free medium to address the needs of specific population groups, at the same time reducing the production costs of this essential vitamin.

Novel Pathway for Corrinoid Compounds Production in Lactobacillus

Vitamin B₁₂ or cobalamin is an essential metabolite for humans, which makes it an interesting compound for many research groups that focus in different producer-strains synthesis pathways. In this work, we report the influence of key intermediaries for cobalamin synthesis added to the culture medium in two Lactobacillus (L.) strains, L. reuteri CRL 1098 and L. coryniformis CRL 1001. Here, we report that addition of Co²⁺ and 5,6-dimethylbenzimidazole increased the corrinoid compounds production in both strains while addition of L-threonine increased only the corrinoid compounds production by CRL 1001 strain. Then, we purified and characterized by LC-MS the corrinoid compounds obtained. Physiological studies besides in silico analysis revealed that L. reuteri CRL 1098 and L. coryniformis CRL 1001 follow different pathways for the last steps of the corrinoid compounds synthesis.

Engineering a vitamin B12 high-throughput screening system by riboswitch sensor in Sinorhizobium meliloti

Background

As a very important coenzyme in the cell metabolism, Vitamin B₁₂ (cobalamin, VB₁₂) has been widely used in food and medicine fields. The complete biosynthesis of VB₁₂ requires approximately 30 genes, but overexpression of these genes did not result in expected increase of VB₁₂ production. High-yield VB₁₂-producing strains are usually obtained by mutagenesis treatments, thus developing an efficient screening approach is urgently needed.

Result

By the help of engineered strains with varied capacities of VB₁₂ production, a riboswitch library was constructed and screened, and the btuB element from Salmonella typhimurium was identified as the best regulatory device. A flow cytometry high-throughput screening system was developed based on the btuB riboswitch with high efficiency to identify positive mutants. Mutation of Sinorhizobium meliloti (S. meliloti) was optimized using the novel mutation technique of atmospheric and room temperature plasma (ARTP). Finally, the mutant S. meliloti MC5–2 was obtained and considered as a candidate for industrial applications. After 7 d’s cultivation on a rotary shaker at 30 °C, the VB₁₂ titer of S. meliloti MC5–2 reached 156 ± 4.2 mg/L, which was 21.9% higher than that of the wild type strain S. meliloti 320 (128 ± 3.2 mg/L). The genome of S. meliloti MC5–2 was sequenced, and gene mutations were identified and analyzed.

Conclusion

To our knowledge, it is the first time that a riboswitch element was used in S. meliloti. The flow cytometry high-throughput screening system was successfully developed and a high-yield VB₁₂ producing strain was obtained. The identified and analyzed gene mutations gave useful information for developing high-yield strains by metabolic engineering. Overall, this work provides a useful high-throughput screening method for developing high VB₁₂-yield strains.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0441-2) contains supplementary material, which is available to authorized users.

Propionibacterium spp.-source of propionic acid, vitamin B12, and other metabolites important for the industry

Bacteria from the Propionibacterium genus consists of two principal groups: cutaneous and classical. Cutaneous Propionibacterium are considered primary pathogens to humans, whereas classical Propionibacterium are widely used in the food and pharmaceutical industries. Bacteria from the Propionibacterium genus are capable of synthesizing numerous valuable compounds with a wide industrial usage. Biomass of the bacteria from the Propionibacterium genus constitutes sources of vitamins from the B group, including B12, trehalose, and numerous bacteriocins. These bacteria are also capable of synthesizing organic acids such as propionic acid and acetic acid. Because of GRAS status and their health-promoting characteristics, bacteria from the Propionibacterium genus and their metabolites (propionic acid, vitamin B12, and trehalose) are commonly used in the cosmetic, pharmaceutical, food, and other industries. They are also used as additives in fodders for livestock. In this review, we present the major species of Propionibacterium and their properties and provide an overview of their functions and applications. This review also presents current literature concerned with the possibilities of using Propionibacterium spp. to obtain valuable metabolites. It also presents the biosynthetic pathways as well as the impact of the genetic and environmental factors on the efficiency of their production.

Research on the ability of propionic acid and vitamin B12 biosynthesis by Propionibacterium freudenreichii strain T82

The purpose of this study was to determine the potential for biosynthesis of propionic acid and vitamin B12 by Propionibacterium freudenreichii T82 in a medium containing various sources of carbon (glucose, fructose, and saccharose). These sugars are present in apple pomaces, which are the waste from the production of apple juice. Using statistical analysis design of experiments (DoE), the results allowed us to determine which sugars (carbon sources) exert the most beneficial influence on the biosynthesis of propionic acid and cobalamin. The highest production of propionic acid by the tested bacterial strain was obtained in a medium in which glucose accounted for at least 50% of the available carbon sources. Depending on the culture medium, the concentration of this metabolite ranged from 23 to 40 g/L. P. freudenreichii T82 produced the smallest amount of acid in medium in which the dominant nutrient source was saccharose. The results obtained indicated an inverse relationship between the amount of acid produced by the bacteria and vitamin B12 biosynthesis. Because of the high efficiency of propionic acid biosynthesis by P. freudenreichii T82, the prospect of using this strain to obtain propionate with the simultaneous disposal of waste materials (such as apple pomaces) which contain glucose and/or fructose is very promising.

Dairy Propionibacteria: Versatile Probiotics

Dairy propionibacteria are used as cheese ripening starters, as biopreservative and as beneficial additives, in the food industry. The main species, Propionibacterium freudenreichii, is known as GRAS (Generally Recognized As Safe, USA, FDA). In addition to another dairy species, Propionibacterium acidipropionici, they are included in QPS (Qualified Presumption of Safety) list. Additional to their well-known technological application, dairy propionibacteria increasingly attract attention for their promising probiotic properties. The purpose of this review is to summarize the probiotic characteristics of dairy propionibacteria reported by the updated literature. Indeed, they meet the selection criteria for probiotic bacteria, such as the ability to endure digestive stressing conditions and to adhere to intestinal epithelial cells. This is a prerequisite to bacterial persistence within the gut. The reported beneficial effects are ranked according to property’s type: microbiota modulation, immunomodulation, and cancer modulation. The proposed molecular mechanisms are discussed. Dairy propionibacteria are described as producers of nutraceuticals and beneficial metabolites that are responsible for their versatile probiotic attributes include short chain fatty acids (SCFAs), conjugated fatty acids, surface proteins, and 1,4-dihydroxy-2-naphtoic acid (DHNA). These metabolites possess beneficial properties and their production depends on the strain and on the growth medium. The choice of the fermented food matrix may thus determine the probiotic properties of the ingested product. This review approaches dairy propionibacteria, with an interest in both technological abilities and probiotic attributes.

Microbial production of vitamin B12: a review and future perspectives

Vitamin B12 is an essential vitamin that is widely used in medical and food industries. Vitamin B12 biosynthesis is confined to few bacteria and archaea, and as such its production relies on microbial fermentation. Rational strain engineering is dependent on efficient genetic tools and a detailed knowledge of metabolic pathways, regulation of which can be applied to improve product yield. Recent advances in synthetic biology and metabolic engineering have been used to efficiently construct many microbial chemical factories. Many published reviews have probed the vitamin B12 biosynthetic pathway. To maximize the potential of microbes for vitamin B12 production, new strategies and tools are required. In this review, we provide a comprehensive understanding of advances in the microbial production of vitamin B12, with a particular focus on establishing a heterologous host for the vitamin B12 production, as well as on strategies and tools that have been applied to increase microbial cobalamin production. Several worthy strategies employed for other products are also included.

Metabolic engineering of Propionibacterium freudenreichii subsp. shermanii for xylose fermentation

Propionibacterium freudenreichii cannot use xylose, the second most abundant sugar in lignocellulosic biomass. Although Propionibacterium acidipropionici can use xylose as a carbon source, it is difficult to genetically modify, impeding further improvement through metabolic engineering. This study identified three xylose catabolic pathway genes encoding for xylose isomerase (xylA), xylose transporter (xylT), and xylulokinase (xylB) in P. acidipropionici and overexpressed them in P. freudenreichii subsp. shermanii via an expression plasmid pKHEM01, enabling the mutant to utilize xylose efficiently even in the presence of glucose without glucose-induced carbon catabolite repression. The mutant showed similar fermentation kinetics with glucose, xylose, and the mixture of glucose and xylose, respectively, as carbon source, and with or without the addition of antibiotic for selection pressure. The engineered P. shermanii thus can provide a novel cell factory for industrial production of propionic acid and other value-added products from lignocellulosic biomass.

The Online Morphology Control and Dynamic Studies on Improving Vitamin B12 Production by Pseudomonas denitrificans with Online Capacitance and Specific Oxygen Consumption Rate

The relationship between the morphological character of Pseudomonas denitrificans and vitamin B12 synthesis based on real-time capacitance measurement and online specific oxygen consumption rate (Q O2) control was established for enhancing vitamin B12 production. Results demonstrated that the threshold Q O2 value lower than 2.0 mmol/gDCW/l would greatly stimulate the state transfer from the cell number growth phase to the cell elongation phase and promote rapid vitamin B12 biosynthesis, while the vitamin B12 biosynthesis rate could also be inhibited when the rate of cell's length-to-width ratio (ratio-LW) was higher than 10:1. Furthermore, the optimal morphology controlling strategy was achieved based on online Q O2 control, which increases the appropriate active cell numbers at the former phase, and then control the elongation of ratio-LW no more than 10:1 at the vitamin B12 biosynthesis phase. The maximal vitamin B12 production reached 239.7 mg/l at 168 h, which was improved by 14.7 % compared with the control (208 mg/l). This online controlling strategy would be effectively applied for improving industrial vitamin B12 fermentation.