Microbial synthesis of cobamides

Identification of vitamin B12 producing bacteria based on the presence of bluB/cobT2 homologues

OBJECTIVES

The objective of the study was to develop a strategy for the identification of new vitamin B₁₂-producing species and to characterize their production capability using a fast and sensitive LC-MS/MS method developed in this study.

RESULTS

Searching for homologues of the bluB/cobT2 fusion gene known to be responsible for the production of the active vitamin B₁₂ form in P. freudenreichii was shown to be a successful strategy for the identification of new vitamin B₁₂-producing strains. The analysis of the identified strains via LC-MS/MS showed the ability of Terrabacter sp. DSM102553, Yimella lutea DSM19828 and Calidifontibacter indicus DSM22967 to produce the active form of vitamin B₁₂. Further analysis of vitamin B₁₂ production capability of Terrabacter sp. DSM102553 in M9 minimal medium and peptone-based media revealed that the highest yield of 2.65 µg of vitamin B₁₂ per g dry cell weight was obtained in M9 medium.

CONCLUSIONS

The proposed strategy enabled identification of Terrabacter sp. DSM102553, whose relatively high yields obtained in the minimal medium open new perspectives for the possible application of the strain for biotechnological vitamin B₁₂ production.

Methylotrophic bacteria with cobalamin-dependent mutases in primary metabolism as potential strains for vitamin B12 production

Several bacterial species are known for their ability to synthesize vitamin B12 but biotechnological vitamin B12 production today is restricted to Pseudomonas denitrificans and Propionibacterium freudenreichii. Nevertheless, the rising popularity of veganism leads to a growing demand for vitamin B12 and thereby interest in alternative strains which can be used as efficient vitamin B12 sources. In this work, we demonstrate that methylotrophic microorganisms which utilize the ethylmalonyl-CoA pathway containing B12-dependent enzymes are capable of active vitamin B12 production. Several bacteria with an essential function of the pathway were tested for vitamin B12 synthesis. Among the identified strains, Hyphomicrobium sp. DSM3646 demonstrated the highest vitamin B12 levels reaching up to 17.9 ± 5.05 µg per g dry cell weight. These relatively high vitamin B12 concentrations achieved in simple cultivation experiments were performed in a mineral methanol medium, which makes Hyphomicrobium sp. DSM3646 a new promising cobalamin-producing strain.

Perspective: Practical Approach to Preventing Subclinical B12 Deficiency in Elderly Population

Vitamin B12 (also known as cobalamin) is an essential water-soluble vitamin that plays a pivotal role for several physiologic functions during one's lifespan. Only certain microorganisms are able to synthetize B12, thus humans obtain cobalamin exclusively from their diet, specifically from animal-derived foods. Specific sub-group populations are at risk of vitamin B12 subclinical deficiency due to different factors including poor intake of animal source foods and age-dependent decrease in the capacity of intestinal B12 uptake. Consumption of animal products produces some negative health issues and negatively impacts sustainability while a plant-based diet increases the risk of B12 deficiency. Taking a cue from the aforementioned considerations, this narrative review aims to summarize facts about B12 deficiency and the burden of inadequate dietary intake in elderly population, as well as to discuss sustainable approaches to vitamin B12 deficiency in aging population.

Microalgal assimilation of vitamin B12 toward the production of a superfood

A network of components from different metabolic pathways is the building scaffold of an indispensable compound in the human organism-vitamin B₁₂ . The biosynthesis of this compound is restricted to a limited number of representatives of bacteria and archaea, while vitamin B₁₂ -dependent enzymes are spread through several domains of life. Different attempts have been performed to increase vitamin B₁₂ levels in dietary products, particularly in vegetarian and vegan dietary regimes. The integration of vitamin B₁₂ in microalgae through symbiosis with microorganisms generally recognized as safe, for example the probiotic Lactobacillus reuteri, can even increase the nutritional value of the microalgal biomass. This study reviews the microbial production of vitamin B₁₂ based on genetic analyses and chemical studies. Recent genetic approaches are focused, particularly potential metabolic engineering targets to increase vitamin B₁₂ production. The bioincorporation of vitamin B₁₂ in microalgae as an attempt to provide a superfood is also reviewed. PRACTICAL APPLICATIONS: Novel food habits (i.e., vegan lifestyle) may lack relevant nutrients, including vitamin B₁₂ . Therefore, there is an increased demand for dietary products rich in vitamin B₁₂ . Of potential interest is the provision of microbial-based superfood rich in numerous nutrients, including this vitamin. This manuscript provides an in-depth and timely overview on vitamin B₁₂ biosynthesis and the major advances on metabolic engineering for improved vitamin B₁₂ production by probiotic bacteria and other microorganisms generally recognized as safe. A relevant advance would result from the bioincorporation of vitamin B₁₂ in alternative microorganisms (non-vitamin B₁₂ producers) increasingly recognized as superfood, that is microalgae.

Cobalamin is produced by Acetobacter pasteurianus DSM 3509

Only a few cobalamin-producing bacterial species are known which are suitable for food fermentations. The strain of Acetobacter pasteurianus DSM 3509 was found to have the capability to synthesize cobalamin. A survival test and a preliminary genetic study of the gene of uroporphyrinogen-III synthase indicated the ability to synthesize cobalamin. By a modified microbiological assay based on Lactobacillus delbrueckii ssp. lactis DSM 20355, 4.57 ng/mL of cyanocorrinoids and 0.75 ng/mL of noncorrinoid growth factors were detected. The product extracted and isolated by immunoaffinity chromatography in its cyanide form had the similar UV spectrum as standard cyanocobalamin and Coα-[α-(7-adenyl)]-(Coβ-cyano) cobamide also known as pseudovitamin B₁₂ produced by Lactobacillus reuteri DSM 20016. The chromatographically separated product of A. pasteurianus was subjected to mass spectrometrical analysis. There, its fragmentation pattern turned out to be equivalent to that of cyanocobalamin also produced by Propionibacterium freudenreichii ssp. freudenreichii DSM 20271 and clearly differs from pseudovitamin B₁₂. Due to the presence of this species in several food applications, there might be cobalamin residues in food fermented with these bacteria.

Streptomyces metabolites in divergent microbial interactions

Streptomyces and related bacteria produce a wide variety of secondary metabolites. Of these, many compounds have industrial applications, but the question of why this group of microorganism produces such various kinds of biologically active substances has not yet been clearly answered. Here, we overview the results from our studies on the novel function and role of Streptomyces metabolites. The diverged action of negative and positive influences onto the physiology of various microorganisms infers the occurrence of complex microbial interactions due to the effect of small molecules produced by Streptomyces. The interactions may serve as a basis for the constitution of biological community.

Bromochloromethane, a Methane Analogue, Affects the Microbiota and Metabolic Profiles of the Rat Gastrointestinal Tract

Bromochloromethane (BCM), an inhibitor of methanogenesis, has been used in animal production. However, little is known about its impact on the intestinal microbiota and metabolic patterns. The present study aimed to investigate the effect of BCM on the colonic bacterial community and metabolism by establishing a Wistar rat model. Twenty male Wistar rats were randomly divided into two groups (control and treated with BCM) and raised for 6 weeks. Bacterial fermentation products in the cecum were determined, and colonic methanogens and sulfate-reducing bacteria (SRB) were quantified. The colonic microbiota was analyzed by pyrosequencing of the 16S rRNA genes, and metabolites were profiled by gas chromatography and mass spectrometry. The results showed that BCM did not affect body weight and feed intake, but it did significantly change the intestinal metabolic profiles. Cecal protein fermentation was enhanced by BCM, as methylamine, putrescine, phenylethylamine, tyramine, and skatole were significantly increased. Colonic fatty acid and carbohydrate concentrations were significantly decreased, indicating the perturbation of lipid and carbohydrate metabolism by BCM. BCM treatment decreased the abundance of methanogen populations, while SRB were increased in the colon. BCM did not affect the total colonic bacterial counts but significantly altered the bacterial community composition by decreasing the abundance of actinobacteria, acidobacteria, and proteobacteria. The results demonstrated that BCM treatment significantly altered the microbiotic and metabolite profiles in the intestines, which may provide further information on the use of BCM in animal production.

A riboswitch sensor to determine vitamin B12 in fermented foods

We describe a sensitive and selective method for determination of vitamin B12 content in fermented foods using riboswitch sensor. A riboswitch amplicon from Propionibacterium freudenreichii was cloned in p519NGFP vector in Escherichia coli BL21 (DE3). The expression of green fluorescence protein was revers correlated to the concentrations of adenosylcobalamin. Adenosylcobalamin directly binds to riboswitch region leading to conformational changes in the secondary structure of mRNA, thus inhibiting expression. After various examinations, a standard curve was obtained from 10 to 1000 ng/mL of cyanocobalamin. The limit of determination is 10 ng/mL. The inter-assay coefficients of variation were 7.5% for the range of 10-1000 ng/mL. The recovery of this method was 92.3%. This method has no or less responses to nucleic acid, pseudovitamin B12, vitamin B12 bound to intrinsic factor and haptocorrin. The riboswitch sensor results were similar with HPLC, but they were Ca. 24% lower than the microbiological assay results.

A bioassay for the detection of benzimidazoles reveals their presence in a range of environmental samples

Cobamides are a family of enzyme cofactors that include vitamin B₁₂ (cobalamin) and are produced solely by prokaryotes. Structural variability in the lower axial ligand has been observed in cobamides produced by diverse organisms. Of the three classes of lower ligands, the benzimidazoles are uniquely found in cobamides, whereas the purine and phenolic bases have additional biological functions. Many organisms acquire cobamides by salvaging and remodeling cobamides or their precursors from the environment. These processes require free benzimidazoles for incorporation as lower ligands, though the presence of benzimidazoles in the environment has not been previously investigated. Here, we report a new purification method and bioassay to measure the total free benzimidazole content of samples from microbial communities and laboratory media components. The bioassay relies on the “calcofluor-bright” phenotype of a bluB mutant of the model cobalamin-producing bacterium Sinorhizobium meliloti. The concentrations of individual benzimidazoles in these samples were measured by liquid chromatography-tandem mass spectrometry. Several benzimidazoles were detected in subpicomolar to subnanomolar concentrations in host-associated and environmental samples. In addition, benzimidazoles were found to be common contaminants of laboratory media components. These results suggest that benzimidazoles present in the environment and in laboratory media have the potential to influence microbial metabolic activities.

Vitamin B12 regulates photosystem gene expression via the CrtJ antirepressor AerR in Rhodobacter capsulatus

The tetrapyrroles haem, bacteriochlorophyll and cobalamin (B12 ) exhibit a complex interrelationship regarding their synthesis. In this study, we demonstrate that AerR functions as an antirepressor of the tetrapyrrole regulator CrtJ. We show that purified AerR contains B12 that is bound to a conserved histidine (His145) in AerR. The interaction of AerR to CrtJ was further demonstrated in vitro by pull down experiments using AerR as bait and quantified using microscale thermophoresis. DNase I DNA footprint assays show that AerR containing B12 inhibits CrtJ binding to the bchC promoter. We further show that bchC expression is greatly repressed in a B12 auxotroph of Rhodobacter capsulatus and that B12 regulation of gene expression is mediated by AerR's ability to function as an antirepressor of CrtJ. This study thus provides a mechanism for how the essential tetrapyrrole, cobalamin controls the synthesis of bacteriochlorophyll, an essential component of the photosystem.

Substitution of Co alpha-(5-hydroxybenzimidazolyl)cobamide (factor III) by vitamin B12 in Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum grown on mineral medium contains 120 nmol of Co alpha-(5-hydroxybenzimidazolyl)cobamides (derivatives of factor III) per g of dry cell mass as the sole cobamide. The bacterium assimilated several corrinoids and benzimidazole bases during autotrophic growth. The corrinoids were converted into factor III; however, after three transfers in 5,6-dimethylbenzimidazole (200 microM)-supplemented mineral medium, derivatives of factor III were completely replaced by derivatives of vitamin B12, which is atypical for methanogens. The total cobamide content of these cells and their growth rate were not affected compared with factor III-containing cells. Therefore, the high cobamide content rather than a particular type of cobamide is required for metabolism of methanogens. Derivatives of factor III are not essential cofactors of cobamide-containing enzymes from methanogenic bacteria, but they are the result of a unique biosynthetic ability of these archaebacteria. The cobamide biosynthesis include unspecific enzymes, which made it possible either to convert non-species-derived corrinoids into derivatives of factor III or to synthesize other types of cobamides than factor III. The cobamide biosynthesis is regulated by its end product. In addition, the uptake of extracellular cobamides is controlled, and the assimilated corrinoids regulate cellular cobamide biosynthesis.

The microbial biosynthesis of methionine

1. The enzymes leading to the methylation of homocysteine have been examined in three micro-organisms: a cobalamin-producing bacterium, Bacillus megaterium; a yeast, Candida utilis; and a basidiomycete fungus, Coprinus lagopus. The yeast and the fungus contain negligible endogenous cobalamin. 2. Extracts of each organism catalyse C(1)-transfer from serine to homocysteine with a polyglutamate folate coenzyme. 3. The enzymes generating the methyl group of methionine from C-3 of serine have similar properties in each case, but different mechanisms of homocysteine transmethylation from 5-methyltetrahydrofolates were found. 4. B. megaterium contains an enzyme with properties suggestive of a vitamin B(12)-dependent homocysteine transmethylase, whereas Cand. utilis and Cop. lagopus transfer the methyl group by a reaction characteristic of the cobalamin-independent mechanism established for Escherichia coli. 5. The specificity of each transmethylase for a 5-methyltetrahydropteroylpolyglutamate is consistent with the results of analyses of endogenous folates in these organisms, which showed only conjugated forms. 6. None of the extracts catalysed methionine production from S-adenosylmethionine and homocysteine. 7. These results are compared with results now available for methionine synthesis in other organisms, which show a considerable diversity of mechanisms.

Vitamin B12 uptake by intestinal microorganisms: mechanism and relevance to syndromes of intestinal bacterial overgrowth

The mechanism of bacterial uptake of vitamin B(12), the spectrum of microorganisms capable of such uptake, and the factors involved were the subject of this study. Bacterial uptake of vitamin B(12) was found to be at least a two stage process. A primary uptake phase which was rapid (1 min or less), pH dependent, nontemperature dependent, did not require viable organisms and was insensitive to either the metabolic inhibitor dinitrophenol or to the sulfhydryl inhibitor N-ethyl-maleimide. Protein denaturation (formalin treatment or autoclaving) abolished all B(12) uptake. This primary uptake phase is thought to represent adsorption to binding or "receptor" sites on the cell wall. Second stage uptake was slower, pH and temperature dependent, required living bacteria, and was abolished by either dinitrophenol or N-ethyl-maleimide. This phase is dependent upon metabolic processes and may reflect transfer of B(12) from surface "receptor" sites into the bacterial cell. Although differences among organisms were observed in total 1 hr uptake, number of surface "receptor" sites, and relative avidities for B(12), all organisms except Streptococcus fecalis shared the two stage mechanism. Two Gram-positive organisms. Bacillus subtilis and Group A streptococcus, demonstrated the highest 1 hr vitamin B(12) uptake values; Gram-negative bacteria required 2,000-10,000 the number of organisms for comparable uptake. Binding constants (K(m)) varied from 5.05 +/-1.67 x 10(-10)M for B. subtilis to 6.18 +/-3.08 x 10(-9)M for Klebsiella pneumoniae which approximate the Km for human intrinsic factor (0.38 x 10(-10)M). Competition between bacteria and intrinsic factor for vitamin B(12) may be inferred from the similarity of these constants. These observations suggest that a variety of enteric and nonenteric organisms, not requiring exogenous B(12), may play a role in the pathogenesis of the vitamin B(12) malabsorption found in the intestinal bacterial overgrowth syndromes.