Metabolic engineering of cobalamin (vitamin B12) production in Bacillus megaterium

Strategy for Optimizing Vitamin B12 Production in Pseudomonas putida KT2440 Using Metabolic Modeling

Background/Objectives: Vitamin B12 is very important for human health, as it is a cofactor for enzymatic activities and plays various roles in human physiology. It is highly valued in the pharmaceutical, food, and additive production industries. Some of the bacteria currently used for the vitamin production are difficult to modify with gene-editing tools and may have slow growth. We propose the use of the bacteria Pseudomonas putida KT2440 for the production of vitamin B12 because it has a robust chassis for genetic modifications. The present wok evaluates P. putida KT2440 as a host for vitamin B12 production and explore potential gene-editing optimization strategies. Methods: We curated and modified a genome-scale metabolic model of Pseudomonas putida KT2440 and evaluated different strategies to optimize vitamin B12 production using the knockin and OptGene algorithms from the COBRA Toolbox. Furthermore, we examined the presence of riboswitches as cis-regulatory elements and calculated theoretical biomass growth yields and vitamin B12 production using a flux balance analysis (FBA). Results: According to the flux balance analysis of P. putida KT2440 under culture conditions, the biomass production values could reach 1.802 gDW-1·h1·L-1, and vitamin B12 production could reach 0.359 µmol·gDW-1·h-1·L-1. The theoretical vitamin B12 synthesis rate calculated using P. putida KT2040 with two additional reactions was 14 times higher than that calculated using the control, Pseudomonas denitrificans, which has been used for the industrial production of this vitamin. Conclusions: We propose that, with the addition of aminopropanol linker genes and the modification of riboswitches, P. putida KT2440 may become a suitable host for the industrial production of vitamin B12.

Biological properties of vitamin B12

Vitamin B12, cobalamin, is indispensable for humans owing to its participation in two biochemical reactions: the conversion of l-methylmalonyl coenzyme A to succinyl coenzyme A, and the formation of methionine by methylation of homocysteine. Eukaryotes, encompassing plants, fungi, animals and humans, do not synthesise vitamin B12, in contrast to prokaryotes. Humans must consume it in their diet. The most important sources include meat, milk and dairy products, fish, shellfish and eggs. Due to this, vegetarians are at risk to develop a vitamin B12 deficiency and it is recommended that they consume fortified food. Vitamin B12 behaves differently to most vitamins of the B complex in several aspects, e.g. it is more stable, has a very specific mechanism of absorption and is stored in large amounts in the organism. This review summarises all its biological aspects (including its structure and natural sources as well as its stability in food, pharmacokinetics and physiological function) as well as causes, symptoms, diagnosis (with a summary of analytical methods for its measurement), prevention and treatment of its deficiency, and its pharmacological use and potential toxicity.

Flux optimization using multiple promoters in Halomonas bluephagenesis as a model chassis of the next generation industrial biotechnology

Predictability and robustness are challenges for bioproduction because of the unstable intracellular synthetic activities. With the deeper understanding of the gene expression process, fine-tuning has become a meaningful tool for biosynthesis optimization. This study characterized several gene expression elements and constructed a multiple inducible system that responds to ten different small chemical inducers in halophile bacterium Halomonas bluephagenesis. Genome insertion of regulators was conducted for the purpose of gene cluster stabilization and regulatory plasmid simplification. Additionally, dynamic ranges of the multiple inducible systems were tuned by promoter sequence mutations to achieve diverse scopes for high-resolution gene expression control. The multiple inducible system was successfully employed to precisely control chromoprotein expression, lycopene and poly-3-hydroxybutyrate (PHB) biosynthesis, resulting in colorful bacterial pictures, optimized cell growth, lycopene and PHB accumulation. This study demonstrates a desirable approach for fine-tuning of rational and efficient gene expressions, displaying the significance for metabolic pathway optimization.

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.

Cobalamin Riboswitches Are Broadly Sensitive to Corrinoid Cofactors to Enable an Efficient Gene Regulatory Strategy

In bacteria, many essential metabolic processes are controlled by riboswitches, gene regulatory RNAs that directly bind and detect metabolites. Highly specific effector binding enables riboswitches to respond to a single biologically relevant metabolite. Cobalamin riboswitches are a potential exception because over a dozen chemically similar but functionally distinct cobalamin variants (corrinoid cofactors) exist in nature. Here, we measured cobalamin riboswitch activity in vivo using a Bacillus subtilis fluorescent reporter system and found, among 38 tested riboswitches, a subset responded to corrinoids promiscuously, while others were semiselective. Analyses of chimeric riboswitches and structural models indicate, unlike other riboswitch classes, cobalamin riboswitches indirectly differentiate among corrinoids by sensing differences in their structural conformation. This regulatory strategy aligns riboswitch-corrinoid specificity with cellular corrinoid requirements in a B. subtilis model. Thus, bacteria can employ broadly sensitive riboswitches to cope with the chemical diversity of essential metabolites. IMPORTANCE Some bacterial mRNAs contain a region called a riboswitch which controls gene expression by binding to a metabolite in the cell. Typically, riboswitches sense and respond to a limited range of cellular metabolites, often just one type. In this work, we found the cobalamin (vitamin B₁₂) riboswitch class is an exception, capable of sensing and responding to multiple variants of B₁₂-collectively called corrinoids. We found cobalamin riboswitches vary in corrinoid specificity with some riboswitches responding to each of the corrinoids we tested, while others responding only to a subset of corrinoids. Our results suggest the latter class of riboswitches sense intrinsic conformational differences among corrinoids in order to support the corrinoid-specific needs of the cell. These findings provide insight into how bacteria sense and respond to an exceptionally diverse, often essential set of enzyme cofactors.

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.

Production of Vitamin K by Wild-Type and Engineered Microorganisms

Vitamin K is a fat-soluble vitamin that mainly exists as phylloquinone or menaquinone in nature. Vitamin K plays an important role in blood clotting and bone health in humans. For use as a nutraceutical, vitamin K is produced by natural extraction, chemical synthesis, and microbial fermentation. Natural extraction and chemical synthesis methods for vitamin K production have limitations, such as low yield of products and environmental concerns. Microbial fermentation is a more sustainable process for industrial production of natural vitamin K than two other methods. Recent advanced genetic technology facilitates industrial production of vitamin K by increasing the yield and productivity of microbial host strains. This review covers (i) general information about vitamin K and microbial host, (ii) current titers of vitamin K produced by wild-type microorganisms, and (iii) vitamin K production by engineered microorganisms, including the details of strain engineering strategies. Finally, current limitations and future directions for microbial production of vitamin K are also discussed.

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 Flux Analysis of Simultaneous Production of Vitamin B12 and Propionic Acid in a Coupled Fermentation Process by Propionibacterium freudenreichii

The metabolic processes involved in simultaneous production of vitamin B12 and propionic acid by Propionibacterium freudenreichii are very complicated. To further investigate the regulatory mechanism of this metabolism, a simplified metabolic network was established. The effects of glucose feeding, propionic acid removal, and 5,6-dimethylbenzimidazole (DMB) addition on the metabolic flux distribution were investigated. The results showed that synthesis of propionic acid can be increased by increasing the metabolic flux through the oxaloacetate and methylmalonyl-CoA branches in the early and middle stages of the coupled fermentation. After DMB addition, the synthesis of vitamin B12 was significantly enhanced via increased metabolic flux through the δ-aminolevulinate branch, which promoted the synthesis of uroporphyrinogen III, a precursor of vitamin B12. Therefore, the analysis of metabolic flux at key nodes can provide theoretical guidance for the optimization of P. freudenreichii fermentation processes. In an experimental coupled fermentation process, the concentrations of vitamin B12 and propionic acid reached 21.6 and 50.12 g/L respectively, increased by 105.71% and 73.91% compared with batch fermentation, which provides a new strategy for industrial production.

The "beauty in the beast"-the multiple uses of Priestia megaterium in biotechnology

Abstract

Over 30 years, the Gram-positive bacterium Priestia megaterium (previously known as Bacillus megaterium) was systematically developed for biotechnological applications ranging from the production of small molecules like vitamin B₁₂, over polymers like polyhydroxybutyrate (PHB) up to the in vivo and in vitro synthesis of multiple proteins and finally whole-cell applications. Here we describe the use of the natural vitamin B₁₂ (cobalamin) producer P. megaterium for the elucidation of the biosynthetic pathway and the subsequent systematic knowledge-based development for production purposes. The formation of PHB, a natural product of P. megaterium and potential petro-plastic substitute, is covered and discussed. Further important biotechnological characteristics of P. megaterium for recombinant protein production including high protein secretion capacity and simple cultivation on value-added carbon sources are outlined. This includes the advanced system with almost 30 commercially available expression vectors for the intracellular and extracellular production of recombinant proteins at the g/L scale. We also revealed a novel P. megaterium transcription-translation system as a complementary and versatile biotechnological tool kit. As an impressive biotechnology application, the formation of various cytochrome P450 is also critically highlighted. Finally, whole cellular applications in plant protection are completing the overall picture of P. megaterium as a versatile giant cell factory.

Key points

• The use of Priestia megaterium for the biosynthesis of small molecules and recombinant proteins through to whole-cell applications is reviewed.

• P. megaterium can act as a promising alternative host in biotechnological production processes.

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.

Application of Dual Promoter Expression System for the Enhanced Heparosan Production in Bacillus megaterium

Heparosan, a capsular polysaccharide synthesized by certain pathogenic bacteria, is a promising precursor for heparin production. Heparosan production is catalyzed by the formation of KfiC-KfiA complex and the subsequent action of KfiC and KfiA proteins. Polycistronic expression of kfiC and kfiA in Bacillus megaterium yielded an unbalanced expression of KfiC and KfiA proteins resulted in decreased heparosan production. In this study, dual promoter plasmid system was constructed to increase the expression levels of KfiC and KfiA proteins. Dual promoter plasmid system along with UDP-glucuronic acid pathway overexpression (CADuet-DB) increased the heparosan production to 203 mg/L in shake flask experiments. Batch fermentation of strain CADuet-DB under controlled conditions yielded a maximum heparosan concentration of 627 mg/L, which is 59% higher than strain CA-DB. A modified logistic model is applied to describe the kinetics of heparosan production and biomass growth. Fed batch fermentation resulted in 3-fold enhancement in heparosan concentration (1.96 g/L), compared to batch fermentation. Nuclear magnetic resonance analysis revealed that heparosan from strain CADuet-DB was similar to Escherichia coli K5 heparosan. These results suggested that dual promoter expression system is a promising alternative to polycistronic expression system to produce heparosan in B. megaterium.

Development and application of a highly efficient CRISPR-Cas9 system for genome engineering in Bacillus megaterium

Bacillus megaterium has become increasingly important for the biotechnological production of valuable compounds of industrial and pharmaceutical importance. Despite recent advances in rational strain design of B. megaterium, these studies have been largely impaired by the lack of molecular tools that are not state-of-the-art for comprehensive genome engineering approaches. In the current work, we describe the adaptation of the CRISPR-Cas9 vector pJOE8999 to enable efficient genome editing in B. megaterium. Crucial modifications comprise the exchange of promoter elements and associated ribosomal binding sites as well as the implementation of a 5-fluorouracil based counterselection system to facilitate proper plasmid curing. In addition, the functionality and performance of the new CRISPR-Cas9 vector pMOE was successfully evaluated by chromosomal disruption studies of the endogenous β-galactosidase gene (BMD_2126) and demonstrated an outstanding efficiency of 100 % based on combinatorial pheno- and genotype analyses. Furthermore, pMOE was applied for the genomic deletion of a steroid esterase gene (BMD_2256) that was identified among several other candidates as the gene encoding the esterase, which prevented accumulation of pharmaceutically important glucocorticoid esters. Recombinant expression of the bacterial chloramphenicol acetyltransferase 1 gene (cat1) in the resulting esterase deficient B. megaterium strain ultimately yielded C21-acetylated as well as novel C21-esterified derivates of cortisone.

The requirement for cobalt in vitamin B12: A paradigm for protein metalation

Vitamin B12, cobalamin, is a cobalt-containing ring-contracted modified tetrapyrrole that represents one of the most complex small molecules made by nature. In prokaryotes it is utilised as a cofactor, coenzyme, light sensor and gene regulator yet has a restricted role in assisting only two enzymes within specific eukaryotes including mammals. This deployment disparity is reflected in another unique attribute of vitamin B12 in that its biosynthesis is limited to only certain prokaryotes, with synthesisers pivotal in establishing mutualistic microbial communities. The core component of cobalamin is the corrin macrocycle that acts as the main ligand for the cobalt. Within this review we investigate why cobalt is paired specifically with the corrin ring, how cobalt is inserted during the biosynthetic process, how cobalt is made available within the cell and explore the cellular control of cobalt and cobalamin levels. The partitioning of cobalt for cobalamin biosynthesis exemplifies how cells assist metalation.

Optimization of hydrogenobyrinic acid biosynthesis in Escherichia coli using multi-level metabolic engineering strategies

BACKGROUND

Hydrogenobyrinic acid is a key intermediate of the de-novo aerobic biosynthesis pathway of vitamin B₁₂. The introduction of a heterologous de novo vitamin B₁₂ biosynthesis pathway in Escherichia coli offers an alternative approach for its production. Although E. coli avoids major limitations that currently faced by industrial producers of vitamin B₁₂, such as long growth cycles, the insufficient supply of hydrogenobyrinic acid restricts industrial vitamin B₁₂ production.

RESULTS

By designing combinatorial ribosomal binding site libraries of the hemABCD genes in vivo, we found that their optimal relative translational initiation rates are 10:1:1:5. The transcriptional coordination of the uroporphyrinogen III biosynthetic module was realized by promoter engineering of the hemABCD operon. Knockdown of competitive heme and siroheme biosynthesis pathways by RBS engineering enhanced the hydrogenobyrinic acid titer to 20.54 and 15.85 mg L^-1, respectively. Combined fine-tuning of the heme and siroheme biosynthetic pathways enhanced the hydrogenobyrinic acid titer to 22.57 mg L^-1, representing a remarkable increase of 1356.13% compared with the original strain FH215-HBA.

CONCLUSIONS

Through multi-level metabolic engineering strategies, we achieved the metabolic balance of the uroporphyrinogen III biosynthesis pathway, eliminated toxicity due to by-product accumulation, and finally achieved a high HBA titer of 22.57 mg L^-1 in E. coli. This lays the foundation for high-yield production of vitamin B₁₂ in E. coli and will hopefully accelerate its industrial production.

Auxotrophic Selection Strategy for Improved Production of Coenzyme B12 in Escherichia coli

The production of coenzyme B₁₂ using well-characterized microorganisms, such as Escherichia coli, has recently attracted considerable attention to meet growing demands of coenzyme B₁₂ in various applications. In the present study, we designed an auxotrophic selection strategy and demonstrated the enhanced production of coenzyme B₁₂ using a previously engineered coenzyme B₁₂-producing E. coli strain. To select a high producer, the coenzyme B₁₂-independent methionine synthase (metE) gene was deleted in E. coli, thus limiting its methionine synthesis to only that via coenzyme B₁₂-dependent synthase (encoded by metH). Following the deletion of metE, significantly enhanced production of the specific coenzyme B₁₂ validated the coenzyme B₁₂-dependent auxotrophic growth. Further precise tuning of the auxotrophic system by varying the expression of metH substantially increased the cell biomass and coenzyme B₁₂ production, suggesting that our strategy could be effectively applied to E. coli and other coenzyme B₁₂-producing strains.

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The auxotrophic selection strategy was applied to coenzyme B₁₂ production

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Coenzyme B₁₂-independent methionine synthase was deleted for auxotroph system

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The auxotrophic strategy could significantly enhance the coenzyme B₁₂ production

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Optimization of the auxotroph system further enhanced the coenzyme B₁₂ production

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.

Production of 3-Hydroxypropanoic Acid From Glycerol by Metabolically Engineered Bacteria

3-hydroxypropanoic acid (3-HP) is a valuable platform chemical with a high demand in the global market. 3-HP can be produced from various renewable resources. It is used as a precursor in industrial production of a number of chemicals, such as acrylic acid and its many derivatives. In its polymerized form, 3-HP can be used in bioplastic production. Several microbes naturally possess the biosynthetic pathways for production of 3-HP, and a number of these pathways have been introduced in some widely used cell factories, such as Escherichia coli and Saccharomyces cerevisiae. Latest advances in the field of metabolic engineering and synthetic biology have led to more efficient methods for bio-production of 3-HP. These include new approaches for introducing heterologous pathways, precise control of gene expression, rational enzyme engineering, redirecting the carbon flux based on in silico predictions using genome scale metabolic models, as well as optimizing fermentation conditions. Despite the fact that the production of 3-HP has been extensively explored in established industrially relevant cell factories, the current production processes have not yet reached the levels required for industrial exploitation. In this review, we explore the state of the art in 3-HP bio-production, comparing the yields and titers achieved in different microbial cell factories and we discuss possible methodologies that could make the final step toward industrially relevant cell factories.

Metabolic engineering of Escherichia coli for de novo biosynthesis of vitamin B12

The only known source of vitamin B₁₂ (adenosylcobalamin) is from bacteria and archaea. Here, using genetic and metabolic engineering, we generate an Escherichia coli strain that produces vitamin B₁₂ via an engineered de novo aerobic biosynthetic pathway. In vitro and/or in vivo analysis of genes involved in adenosylcobinamide phosphate biosynthesis from Rhodobacter capsulatus suggest that the biosynthetic steps from co(II)byrinic acid a,c-diamide to adocobalamin are the same in both the aerobic and anaerobic pathways. Finally, we increase the vitamin B₁₂ yield of a recombinant E. coli strain by more than ∼250-fold to 307.00 µg g⁻¹ DCW via metabolic engineering and optimization of fermentation conditions. Beyond our demonstration of E. coli as a microbial biosynthetic platform for vitamin B₁₂ production, our study offers an encouraging example of how the several dozen proteins of a complex biosynthetic pathway can be transferred between organisms to facilitate industrial production.

Vitamin B₁₂ is an essential nutrient with limited natural sources. Here the authors transfer 28 pathway synthesis genes from several bacteria including R. capsulatus to E. coli and, using metabolic engineering and optimised fermentation conditions, achieve high yields.

Rhodobacterales use a unique L-threonine kinase for the assembly of the nucleotide loop of coenzyme B12

Several of the enzymes involved in the conversion of adenosylcobyric acid (AdoCby) to adenosylcobamide (AdoCba) are yet to be identified and characterized in some cobamide (Cba)-producing prokaryotes. Using a bioinformatics approach, we identified the bluE gene (locus tag RSP_0788) of Rhodobacter sphaeroides 2.4.1 as a putative functional homolog of the L-threonine kinase enzyme (PduX, EC 2.7.1.177) of S. enterica. In AdoCba, (R)-1-aminopropan-2-ol O-phosphate (AP-P) links the nucleotide loop to the corrin ring; most known AdoCba producers derive AP-P from L-Thr-O-3-phosphate (L-Thr-P). Here, we show that RsBluE has L-Thr-independent ATPase activity in vivo and in vitro. We used ³¹ P-NMR spectroscopy to show that RsBluE generates L-Thr-P at the expense of ATP and is unable to use L-Ser as a substrate. BluE from R. sphaeroides or Rhodobacter capsulatus restored AdoCba biosynthesis in S. enterica ΕpduX and R. sphaeroides ΕbluE mutant strains. R. sphaeroides ΕbluE strains exhibited a decreased pigment phenotype that was restored by complementation with BluE. Finally, phylogenetic analyses revealed that bluE was restricted to the genomes of a few Rhodobacterales that appear to have a preference for a specific form of Cba, namely Coᴽ-(ᴽ-5,6-dimethylbenzimidazolyl-Coᵦ-adenosylcobamide (a.k.a. adenosylcobalamin, AdoCbl; coenzyme B₁₂ , CoB₁₂ ).

Microbial cell factories for the sustainable manufacturing of B vitamins

Vitamins are essential compounds in human and animal diets. Their demand is increasing globally in food, feed, cosmetics, chemical and pharmaceutical industries. Most current production methods are unsustainable because they use non-renewable sources and often generate hazardous waste. Many microorganisms produce vitamins naturally, but their corresponding metabolic pathways are tightly regulated since vitamins are needed only in catalytic amounts. Metabolic engineering is accelerating the development of microbial cell factories for vitamins that could compete with chemical methods that have been optimized over decades, but scientific hurdles remain. Additional technological and regulatory issues need to be overcome for innovative bioprocesses to reach the market. Here, we review the current state of development and challenges for fermentative processes for the B vitamin group.

Functional annotation of hypothetical proteins from the Exiguobacterium antarcticum strain B7 reveals proteins involved in adaptation to extreme environments, including high arsenic resistance

Exiguobacterium antarcticum strain B7 is a psychrophilic Gram-positive bacterium that possesses enzymes that can be used for several biotechnological applications. However, many proteins from its genome are considered hypothetical proteins (HPs). These functionally unknown proteins may indicate important functions regarding the biological role of this bacterium, and the use of bioinformatics tools can assist in the biological understanding of this organism through functional annotation analysis. Thus, our study aimed to assign functions to proteins previously described as HPs, present in the genome of E. antarcticum B7. We used an extensive in silico workflow combining several bioinformatics tools for function annotation, sub-cellular localization and physicochemical characterization, three-dimensional structure determination, and protein-protein interactions. This genome contains 2772 genes, of which 765 CDS were annotated as HPs. The amino acid sequences of all HPs were submitted to our workflow and we successfully attributed function to 132 HPs. We identified 11 proteins that play important roles in the mechanisms of adaptation to adverse environments, such as flagellar biosynthesis, biofilm formation, carotenoids biosynthesis, and others. In addition, three predicted HPs are possibly related to arsenic tolerance. Through an in vitro assay, we verified that E. antarcticum B7 can grow at high concentrations of this metal. The approach used was important to precisely assign function to proteins from diverse classes and to infer relationships with proteins with functions already described in the literature. This approach aims to produce a better understanding of the mechanism by which this bacterium adapts to extreme environments and to the finding of targets with biotechnological interest.

Genetic-Metabolic Coupling for Targeted Metabolic Engineering

Production of chemicals in microbes often employs potent biosynthetic enzymes, which can interact with the microbial native metabolism to affect cell fitness and product yield. However, production optimization largely relies on data collected from wild-type strains in the absence of metabolic perturbations, thus limiting their relevance to specific conditions. Here, we address this issue by coupling cell fitness to the production of thiamine diphosphate in Escherichia coli using a synthetic RNA biosensor. We use this strategy to interrogate a library of transposon mutants and elucidate the native gene network influencing both cell fitness and thiamine production. Ultimately, we identify effectors of the OxyR-Fur stress response that limit thiamine biosynthesis via alternative regulation of iron storage and Fe-S cluster inclusion in enzymes. This study presents a new approach for the reliable high-throughput identification of genetic targets of both known and unknown function that are directly relevant to a specific biosynthetic process.

CYP109E1 is a novel versatile statin and terpene oxidase from Bacillus megaterium

CYP109E1 is a cytochrome P450 monooxygenase from Bacillus megaterium with a hydroxylation activity for testosterone and vitamin D3. This study reports the screening of a focused library of statins, terpene-derived and steroidal compounds to explore the substrate spectrum of this enzyme. Catalytic activity of CYP109E1 towards the statin drug-precursor compactin and the prodrugs lovastatin and simvastatin as well as biotechnologically relevant terpene compounds including ionones, nootkatone, isolongifolen-9-one, damascones, and β-damascenone was found in vitro. The novel substrates induced a type I spin-shift upon binding to P450 and thus permitted to determine dissociation constants. For the identification of conversion products by NMR spectroscopy, a B. megaterium whole-cell system was applied. NMR analysis revealed for the first time the ability of CYP109E1 to catalyze an industrially highly important reaction, the production of pravastatin from compactin, as well as regioselective oxidations generating drug metabolites (6'β-hydroxy-lovastatin, 3'α-hydroxy-simvastatin, and 4″-hydroxy-simvastatin) and valuable terpene derivatives (3-hydroxy-α-ionone, 4-hydroxy-β-ionone, 11,12-epoxy-nootkatone, 4(R)-hydroxy-isolongifolen-9-one, 3-hydroxy-α-damascone, 4-hydroxy-β-damascone, and 3,4-epoxy-β-damascone). Besides that, a novel compound, 2-hydroxy-β-damascenone, produced by CYP109E1 was identified. Docking calculations using the crystal structure of CYP109E1 rationalized the experimentally observed regioselective hydroxylation and identified important amino acid residues for statin and terpene binding.

Mini review: Recombinant production of tailored bio-pharmaceuticals in different Bacillus strains and future perspectives

Bio-pharmaceuticals like antibodies, hormones and growth factors represent about one-fifth of commercial pharmaceuticals. Host candidates of growing interest for recombinant production of these proteins are strains of the genus Bacillus, long being established for biotechnological production of homologous and heterologous proteins. Bacillus strains benefit from development of efficient expression systems in the last decades and emerge as major industrial workhorses for recombinant proteins due to easy cultivation, non-pathogenicity and their ability to secrete recombinant proteins directly into extracellular medium allowing cost-effective downstream processing. Their broad product portfolio of pharmaceutically relevant recombinant proteins described in research include antibody fragments, growth factors, interferons and interleukins, insulin, penicillin G acylase, streptavidin and different kinases produced in various cultivation systems like microtiter plates, shake flasks and bioreactor systems in batch, fed-batch and continuous mode. To further improve production and secretion performance of Bacillus, bottlenecks and limiting factors concerning proteases, chaperones, secretion machinery or feedback mechanisms can be identified on different cell levels from genomics and transcriptomics via proteomics to metabolomics and fluxomics. For systematical identification of recurring patterns characteristic of given regulatory systems and key genetic targets, systems biology and omics-technology provide suitable and promising approaches, pushing Bacillus further towards industrial application for recombinant pharmaceutical protein production.

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.

A Bacillus megaterium System for the Production of Recombinant Proteins and Protein Complexes

For many years the Gram-positive bacterium Bacillus megaterium has been used for the production and secretion of recombinant proteins. For this purpose it was systematically optimized. Plasmids with different inducible promoter systems, with different compatible origins, with small tags for protein purification and with various specific signals for protein secretion were combined with genetically improved host strains. Finally, the development of appropriate cultivation conditions for the production strains established this organism as a bacterial cell factory even for large proteins. Along with the overproduction of individual proteins the organism is now also used for the simultaneous coproduction of up to 14 recombinant proteins, multiple subsequently interacting or forming protein complexes. Some of these recombinant strains are successfully used for bioconversion or the biosynthesis of valuable components including vitamins. The titers in the g per liter scale for the intra- and extracellular recombinant protein production prove the high potential of B. megaterium for industrial applications. It is currently further enhanced for the production of recombinant proteins and multi-subunit protein complexes using directed genetic engineering approaches based on transcriptome, proteome, metabolome and fluxome data.

5-Aminolevulinic acid production in engineered Corynebacterium glutamicum via C5 biosynthesis pathway

ALA (5-aminolevulinic acid) is an important intermediate in the synthesis of tetrapyrroles and the use of ALA has been gradually increasing in many fields, including medicine and agriculture. In this study, improved biological production of ALA in Corynebacterium glutamicum was achieved by overexpressing glutamate-initiated C5 pathway. For this purpose, copies of the glutamyl t-RNA reductase HemA from several bacteria were mutated by site-directed mutagenesis of which a HemA version from Salmonella typhimurium exhibited the highest ALA production. Cultivation of the HemA-expressing strain produced approximately 204 mg/L of ALA, while co-expression with HemL (glutamate-1-semialdehyde aminotransferase) increased ALA concentration to 457 mg/L, representing 11.6- and 25.9-fold increases over the control strain (17 mg/L of ALA). Further effects of metabolic perturbation were investigated, leading to penicillin addition that further improves ALA production to 584 mg/L. In an optimized flask fermentation, engineered C. glutamicum strains expressing the HemA and hemAL operon produced up to 1.1 and 2.2g/L ALA, respectively, under glutamate-producing conditions. The final yields represent 10.7- and 22.0-fold increases over the control strain (0.1g/L of ALA). From these findings, ALA biosynthesis from glucose was successfully demonstrated and this study is the first to report ALA overproduction in C. glutamicum via metabolic engineering.

Rapid and high-throughput construction of microbial cell-factories with regulatory noncoding RNAs

Due to global crises such as pollution and depletion of fossil fuels, sustainable technologies based on microbial cell-factories have been garnering great interest as an alternative to chemical factories. The development of microbial cell-factories is imperative in cutting down the overall manufacturing cost. Thus, diverse metabolic engineering strategies and engineering tools have been established to obtain a preferred genotype and phenotype displaying superior productivity. However, these tools are limited to only a handful of genes with permanent modification of a genome and significant labor costs, and this is one of the bottlenecks associated with biofactory construction. Therefore, a groundbreaking rapid and high-throughput engineering tool is needed for efficient construction of microbial cell-factories. During the last decade, copious small noncoding RNAs (ncRNAs) have been discovered in bacteria. These are involved in substantial regulatory roles like transcriptional and post-transcriptional gene regulation by modulating mRNA elongation, stability, or translational efficiency. Because of their vulnerability, ncRNAs can be used as another layer of conditional control over gene expression without modifying chromosomal sequences, and hence would be a promising high-throughput tool for metabolic engineering. Here, we review successful design principles and applications of ncRNAs for high-throughput metabolic engineering or physiological studies of diverse industrially important microorganisms.

Role and Function of LitR, an Adenosyl B12-Bound Light-Sensitive Regulator of Bacillus megaterium QM B1551, in Regulation of Carotenoid Production

The LitR/CarH family of proteins is a light-sensitive MerR family of transcriptional regulators that contain an adenosyl B12 (coenzyme B12 or AdoB12)-binding domain at the C terminus. The genes encoding these proteins are found in phylogenetically diverse bacterial genera; however, the biochemical properties of these proteins from Gram-positive bacteria remain poorly understood. We performed genetic and biochemical analyses of a homolog of the LitR protein from Bacillus megaterium QM B1551, a Gram-positive endospore-forming soil bacterium. Carotenoid production was induced by illumination in this bacterium. In vivo analysis demonstrated that LitR plays a central role in light-inducible carotenoid production and serves as a negative regulator of the light-inducible transcription of crt and litR itself. Biochemical evidence showed that LitR in complex with AdoB12 binds to the promoter regions of litR and the crt operon in a light-sensitive manner. In vitro transcription experiments demonstrated that AdoB12-LitR inhibited the specific transcription of the crt promoter generated by a σ(A)-containing RNA polymerase holoenzyme under dark conditions. Collectively, these data indicate that the AdoB12-LitR complex serves as a photoreceptor with DNA-binding activity in B. megaterium QM B1551 and that its function as a transcriptional repressor is fundamental to the light-induced carotenoid production.

IMPORTANCE

Members of the LitR/CarH family are AdoB12-based photosensors involved in light-inducible carotenoid production in nonphototrophic Gram-negative bacteria. Our study revealed that Bacillus LitR in complex with AdoB12 also serves as a transcriptional regulator with a photosensory function, which indicates that the LitR/CarH family is generally involved in the light-inducible carotenoid production of nonphototrophic bacteria.

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

An efficient fermentation-strengthening approach was developed to improve the anaerobic production of vitamin B12 by cultivation process optimization with Propionibacterium freudenreichii. The effects of the byproduct propionic acid and the precursor 5,6-dimethylbenzimidazole (DMB) on vitamin B12 biosynthesis were investigated. Byproduct inhibition experiments showed that maintaining propionic acid concentration in broth below 10-20 g/L in the early stage and 20-30 g/L in the late stage can efficiently improve vitamin B12 biosynthesis. Batch fermentation indicated the occurrence of feed-back inhibition in intracellular intermediate biosynthesis. In addition, the incorporation of the precursor DMB depended on the fermentation level of the vitamin B12 intermediate. High vitamin B12 concentration (58.8 mg/L) and production (0.37 mg/g) were obtained with an expanded bed adsorption bioreactor by using the propionic acid and DMB control method. The optimum concentration and production of 59.5 and 0.59 mg/L h for vitamin B12 production were respectively achieved after five continuous batches.

Development of a two-step cultivation strategy for the production of vitamin B12 by Bacillus megaterium

Background

Vitamin B12 is a fascinating molecule which acts as a co-factor in the metabolism of many organisms, especially affecting DNA synthesis and regulation, fatty acid synthesis and energy production. The synthesis of vitamin B12 is limited to a few of bacteria and archaea. Therefore, industrial microbial fermentation is used to meet annual demands worldwide of vitamin B12 and as an alternative method to the chemical synthesis which requires at least 60 steps that is uneconomical. Bacillus megaterium is one of vitamin B12 producers and an ideal host for many biotechnology applications and being one of the best tools for the industrial production of several enzymes. Therefore, a two-step optimization strategy was established to produce high yield of vitamin B12 by B. megaterium through the provision of the production requirements and the suitable conditions for the biosynthesis of vitamin B12.

Results

We achieved the optimum conditions for the fermentation process of B. megaterium to produce high yield of vitamin B12 in a practical way based on statistical design and analysis which allowed vitamin B12 production to increase up to 759-fold (204.46 μg/l) as compared with control without parameters (0.26 μg/L). High performance liquid chromatography coupled to variable wavelength detector and mass spectrometry has been used to identify vitamin B12 forms and confirm the results.

Conclusions

We developed the fermentation process of B. megaterium to enhance the production of vitamin B12 by providing the required supplements for the synthesis of vitamin B12 (CoCl₂, δ-aminolevulinic acid (ALA) and 5,6-dimethylbenzimidazole (DMB)) and dividing the fermentation process into three stages. In addition, the optimum incubation times of the three fermentation stages were investigated and performed with reducing number of experimental and evaluated multiple parameters and their interactions by using statistical experimental design and analysis. All of these strategies has proven successful in enhancing the production of vitamin B12 up to 204.46 μg/l and demonstrated that B. megaterium could be a good candidate for the industrial production of vitamin B12.

Towards a cell factory for vitamin B12 production in Bacillus megaterium: bypassing of the cobalamin riboswitch control elements

Bacillus megaterium is a bacterium that has been used in the past for the industrial production of vitamin B12 (cobalamin), the anti-pernicious anaemia factor. Cobalamin is a modified tetrapyrrole with a cobalt ion coordinated within its macrocycle. More recently, B. megaterium has been developed as a host for the high-yield production of recombinant proteins using a xylose inducible promoter system. Herein, we revisit cobalamin production in B. megaterium DSM319. We have investigated the importance of cobalt for optimum growth and cobalamin production. The cobaltochelatase (CbiX(L)) is encoded within a 14-gene cobalamin biosynthetic (cbi) operon, whose gene-products oversee the transformation of uroporphyrinogen III into adenosylcobyrinic acid a,c-diamide, a key precursor of cobalamin synthesis. The production of CbiX(L) in response to exogenous cobalt was monitored. The metal was found to stimulate cobalamin biosynthesis and decrease the levels of CbiX(L). From this we were able to show that the entire cbi operon is transcriptionally regulated by a B12-riboswitch, with a switch-off point at approximately 5 nM cobalamin. To bypass the effects of the B12-riboswitch the cbi operon was cloned without these regulatory elements. Growth of these strains on minimal media supplemented with glycerol as a carbon source resulted in significant increases in cobalamin production (up to 200 μg L(-1)). In addition, a range of partially amidated intermediates up to adenosylcobyric acid was detected. These findings outline a potential way to develop B. megaterium as a cell factory for cobalamin production using cheap raw materials.

Bacterial cellular engineering by genome editing and gene silencing

Genome editing is an important technology for bacterial cellular engineering, which is commonly conducted by homologous recombination-based procedures, including gene knockout (disruption), knock-in (insertion), and allelic exchange. In addition, some new recombination-independent approaches have emerged that utilize catalytic RNAs, artificial nucleases, nucleic acid analogs, and peptide nucleic acids. Apart from these methods, which directly modify the genomic structure, an alternative approach is to conditionally modify the gene expression profile at the posttranscriptional level without altering the genomes. This is performed by expressing antisense RNAs to knock down (silence) target mRNAs in vivo. This review describes the features and recent advances on methods used in genomic engineering and silencing technologies that are advantageously used for bacterial cellular engineering.

Tuning primary metabolism for heterologous pathway productivity

Tuning expression of competing endogenous pathways has been identified as an effective strategy in the optimization of heterologous production pathways. However, intervention at the first step of glycolysis, where no alternate routes of carbon utilization exist, remains unexplored. In this work we have engineered a viable E. coli host that decouples glucose transport and phosphorylation, enabling independent control of glucose flux to a heterologous pathway of interest through glucokinase (glk) expression. Using community sourced and curated promoters, glk expression was varied over a 3-fold range while maintaining cellular viability. The effects of glk expression on the productivity of a model glucose-consuming pathway were also studied. Through control of glycolytic flux we were able to explore a number of cellular phenotypes and vary the yield of our model pathway by up to 2-fold in a controllable manner.

Reconstruction and analysis of the industrial strain Bacillus megaterium WSH002 genome-scale in silico metabolic model

A genome-scale metabolic model of Bacillus megaterium WSH002, an industrial bacterium widely used in the vitamin C industry, was reconstructed on the basis of the genome annotation and data from the literature and biochemical databases. It comprises 1112 reactions, 993 metabolites, and 1055 genes, including 43 new annotated genes. This model was able to predict qualitatively and quantitatively the growth of B. megaterium on a range of carbon and nitrogen sources, and the results agreed well with experimental data. A gene essentiality analysis predicted a core metabolic essential gene set of 57 genes on three different media. Furthermore, constraint-based analysis revealed that B. megaterium WSH002 is capable of producing and exporting several key metabolites, which could promote the growth of Ketogulonicigenium vulgare and 2-keto-l-gulonic acid (2-KLG) production. Here, the model represents a helpful tool for understanding and exploring this important industrial organism.

The anaerobic biosynthesis of vitamin B12

Vitamin B12 (cobalamin) is a cobalt-containing modified tetrapyrrole that is an essential nutrient for higher animals. Its biosynthesis is restricted to certain bacteria and requires approximately 30 enzymatic steps for its complete de novo construction. Remarkably, two distinct biosynthetic pathways exist, which are termed the aerobic and anaerobic routes. The anaerobic pathway has yet to be fully characterized due to the inherent instability of its oxygen-sensitive intermediates. Bacillus megaterium, a bacterium previously used for the commercial production of cobalamin, has a complete anaerobic pathway and this organism is now being used to investigate the anaerobic B12 pathway through the application of recent advances in recombinant protein production. The present paper provides a summary of recent findings in the anaerobic pathway and future perspectives.

Getting the big beast to work--systems biotechnology of Bacillus megaterium for novel high-value proteins

The high industrial relevance of the soil bacterium Bacillus megaterium as host for recombinant proteins is driving systems-wide analyses of its metabolic and regulatory networks. The present review highlights novel systems biology tools available to unravel the various cellular components on the level of metabolic and regulatory networks. These provide a rational platform for systems metabolic engineering of B. megaterium. In line, a number of interesting studies have particularly focused on studying recombinant B. megaterium in its industrial bioprocess environment thus integrating systems metabolic engineering with systems biotechnology and providing the full picture toward optimal processes.

Recent advances in microbial production of δ-aminolevulinic acid and vitamin B12

δ-aminolevulinate (ALA) is an important intermediate involved in tetrapyrrole synthesis (precursor for vitamin B12, chlorophyll and heme) in vivo. It has been widely applied in agriculture and medicine. On account of many disadvantages of its chemical synthesis, microbial production of ALA has been received much attention as an alternative because of less expensive raw materials, low pollution, and high productivity. Vitamin B12, one of ALA derivatives, which plays a vital role in prevention of anaemia has also attracted intensive works. In this review, recent advances on the production of ALA and vitamin B12 with novel approaches such as whole-cell enzyme-transformation and metabolic engineering are described. Furthermore, the direction for future research and perspective are also summarized.

Effect of chemical and microbial vitamin B₁₂ analogues on production of vitamin B₁₂

Strain improvement by genetic manipulation or optimization of fermentation conditions for overproduction of vitamin B(12) has a drawback due to feed back inhibition. To resist the feed back inhibition by analogues of vitamin B(12) in Propionibacterium freudenrechii subsps. shermanii (OLP-5), we have tested with microbially separated B(12) analogues from three different strains. Microbial analogues were differentiated from commercially available vitamin B(12) by high pressure liquid chromatography and spectrophotometric method. An analogue isolated from NRRL-B-4327 was shown to increase vitamin B(12) concentration from 18.53 ± 0.15 to 31.67 ± 0.58 mg/l in OLP-5 strain. The presence of chemical analogue (ICH(2) Co(DH)(2) (H(2)Py)(4)) increased vitamin B(12) production from 16.13 ± 0.15 to 18.53 ± 0.15 mg/l in OLP-5. These findings revealed that addition of B(12) analogues in fermentation media have developed strain resistance to feed back inhibition by vitamin B(12).