Interactive performances of betaine on the metabolic processes of Pseudomonas denitrificans

Reprocessing of side-streams towards obtaining valuable bacterial metabolites

Every year, all over the world, the industry generates huge amounts of residues. Side-streams are most often used as feed, landfilled, incinerated, or discharged into sewage. These disposal methods are far from perfect. Taking into account the composition of the side-streams, it seems that they should be used as raw materials for further processing, in accordance with the zero-waste policy and sustainable development. The article describes the latest achievements in biotechnology in the context of bacterial reprocessing of residues with the simultaneous acquisition of their metabolites. The article focuses on four metabolites - bacterial cellulose, propionic acid, vitamin B12 and PHAs. Taking into account global trends (e.g. food, packaging, medicine), it seems that in the near future there will be a sharp increase in demand for this type of compounds. In order for their production to be profitable and commercialised, cheap methods of its obtaining must be developed. The article, in addition to obtaining these bacterial metabolites from side-streams, also discusses e.g. factors affecting their production, metabolic pathways and potential and current applications. The presented chapters provide a complete overview of the current knowledge on above metabolites, which can be helpful for the academic and scientific communities and the several industries. KEY POINTS: • The industry generates millions of tons of organic side-streams each year. • Generated residues burden the natural environment. • A good and cost-effective method of side-streams management seems to be biotechnology - reprocessing with the use of bacteria. • Biotechnological disposal of side-streams gives the opportunity to obtain valuable compounds in cheaper ways: BC, PA, vitmain B12, PHAs.

Shift of Choline/Betaine Pathway in Recombinant Pseudomonas for Cobalamin Biosynthesis and Abiotic Stress Protection

The B12-producing strains Pseudomonas nitroreducens DSM 1650 and Pseudomonas sp. CCUG 2519 (both formerly Pseudomonas denitrificans), with the most distributed pathway among bacteria for exogenous choline/betaine utilization, are promising recombinant hosts for the endogenous production of B12 precursor betaine by direct methylation of bioavailable glycine or non-proteinogenic β-alanine. Two plasmid-based de novo betaine pathways, distinguished by their enzymes, have provided an expression of the genes encoding for N-methyltransferases of the halotolerant cyanobacterium Aphanothece halophytica or plant Limonium latifolium to synthesize the internal glycine betaine or β-alanine betaine, respectively. These betaines equally allowed the recombinant pseudomonads to grow effectively and to synthesize a high level of cobalamin, as well as to increase their protective properties against abiotic stresses to a degree comparable with the supplementation of an exogenous betaine. Both de novo betaine pathways significantly enforced the protection of bacterial cells against lowering temperature to 15 °C and increasing salinity to 400 mM of NaCl. However, the expression of the single plant-derived gene for the β-alanine-specific N-methyltransferase additionally increased the effectiveness of exogenous glycine betaine almost twofold on cobalamin biosynthesis, probably due to the Pseudomonas' ability to use two independent pathways, their own choline/betaine pathway and the plant β-alanine betaine biosynthetic pathway.

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.

Revealing the promoting effect of betaine on vitamin B12 biosynthetic pathway of Pseudomonas denitrificans by using a proteomics analysis

BACKGROUND

Our previous comparative metabolomics research revealed that betaine (N,N,N-trimethylglycine, a typically essential methyl-group donor for vitamin B12 biosynthesis) had a powerful promoting effect on the generation of vitamin B12 precursors and intermediates in vitamin B12-producing Pseudomonas denitrificans. However, the integral effect of betaine on the vitamin B12 biosynthetic pathway is still unclear.

OBJECTIVE

Considering the vitamin B12 biosynthetic pathway of P. denitrificans as a whole, this work aimed to reveal the biological function of betaine on the vitamin B12 biosynthetic pathway in P. denitrificans, which would sharpen and expand the understanding of betaine as the methyl-group donor for vitamin B12 biosynthesis.

MATERIALS AND METHODS

By using a proteomics method based on the iTRAQ technique, the present study compared and analyzed the differential expression of proteins involved in vitamin B12 biosynthetic pathway under 10 g/L betaine addition to P. denitrificans fermentation medium.

RESULTS

The results showed that betaine could significantly up-regulate the expression of proteins related to the vitamin B12 biosynthetic pathway, which was mainly reflected in the following three aspects: 1) the δ-aminolevulinic acid (ALA) synthase and porphobilinogen synthase that were responsible for the formation of the committed precursors for tetrapyrrole-derived macrocycle in vitamin B12 molecule; 2) the C-methylation-related enzymes (such as precorrin-4 C(11)-methyltransferase, Precorrin-2 C(20)-methyltransferase, Precorrin-8X methylmutase, and Precorrin-6Y C5,15-methyltransferase) and methionine synthase that were crucial to the C-methylation reactions for vitamin B12 biosynthesis; 3) the late-stage key enzymes (Cobaltochelatase, and Cob(I)yrinic acid a,c-diamide adenosyltransferase) that were related to cobalt chelation of vitamin B12 molecule.

CONCLUSIONS

The present study clearly demonstrated that betaine could significantly promote the expression of the integral enzymes involved in the vitamin B12 biosynthetic pathway of P. denitrificans, thus promoting vitamin B12 biosynthesis.

Identification of a xylose-inducible promoter and its application for improving vitamin B12 production in Sinorhizobium meliloti

Sinorhizobium meliloti 320 is a vitamin B₁₂ (VB₁₂ ) high-producing strain that has been isolated and identified in our previous study. Because the regulatory toolbox for S. meliloti is limited, we searched for new genetic components and identified the two xylose-inducible promoters P_A and P_B based on a promoter-probe vector with a green fluorescent protein (GFP) as reporter. Compared with the P_araA promoter from S. meliloti, both promoters exhibited higher induced expression and lower basal expression. Subsequently, the influence of glucose or sucrose on the expression of GFP driven by these three promoters was assayed. Glucose repressed all three promoters, and the expression of P_araA was the lowest in the presence of glucose. Although sucrose repressed the expression of P_A by 35% and improved the expression of P_araA by 16%, the expression level of P_A was the highest and was 13% higher than that of P_araA . Lastly, we overexpressed the hemA gene in the C4 pathway using the P_A promoter in S. meliloti 320, and the VB₁₂ production of the engineered strain increased by 11%. The VB₁₂ production was further increased by 11% by adding 0.1% sodium succinate to the culture medium.

Effects of betaine supplementation on L-threonine fed-batch fermentation by Escherichia coli

Betaine can act as a stress protectant, methyl donor, or enzyme stabilizer in vitro for the biosynthesis of structurally complex compounds. The performances of betaine type and concentration on the metabolic processes of Escherichia coli JLTHR in a 5-L fermentor were investigated. The results showed that the maximum L-threonine production of 127.3 g/L and glucose conversion percentage of 58.12% was obtained fed with the glucose solution containing 2 g/L betaine hydrochloride, which increased by 14.5 and 6.87% more compared to that of the control, respectively. This study presents an analysis of the metabolic fluxes of E. coli JLTHR for the production of L-threonine with betaine supplementation. When betaine was fed into the fermentation culture medium, the metabolic flux entering into the pentose phosphate pathway (HMP) and biosynthesis route of L-threonine increased by 57.3 and 10.1%, respectively. In conclusion, exogenous addition of betaine was validated to be a feasible and efficacious approach to improve L-threonine production.