is a very large bacterial genus in which several species can use d-malate for growth. However, the enzymes that can metabolize d-malate, such as d-malate dehydrogenase, appear to be absent in most species. d-3-Phosphoglycerate dehydrogenase (SerA) can catalyze the production of d-2-hydroxyglutarate (d-2-HG) from 2-ketoglutarate to support d-3-phosphoglycerate dehydrogenation, which is the initial reaction in bacterial l-serine biosynthesis. In this study, we show that SerA of the strain A1501 reduces oxaloacetate to d-malate and that d-2-HG dehydrogenase (D2HGDH) from displays d-malate-oxidizing activity. Of note, D2HGDH participates in converting a trace amount of d-malate to oxaloacetate during bacterial l-serine biosynthesis. Moreover, D2HGDH is crucial for the utilization of d-malate as the sole carbon source for growth of A1501. We also found that the D2HGDH expression is induced by the exogenously added d-2-HG or d-malate and that a flavoprotein functions as a soluble electron carrier between D2HGDH and electron transport chains to support d-malate utilization by These results support the idea that D2HGDH evolves as an enzyme for both d-malate and d-2-HG dehydrogenation in In summary, D2HGDH from A1501 participates in both a core metabolic pathway for l-serine biosynthesis and utilization of extracellular d-malate.
Background: Whey is a major pollutant generated by the dairy industry. To decrease environmental pollution caused by the industrial release of whey, new prospects for its utilization need to be urgently explored. Here, we investigated the possibility of using whey powder to produce 2,3-butanediol (BDO), an important platform chemical. Results: Klebsiella oxytoca strain PDL-0 was selected because of its ability to efficiently produce BDO from lactose, the major fermentable sugar in whey. After deleting genes pox, pta, frdA, ldhD, and pflB responding for the production of by-products acetate, succinate, lactate, and formate, a recombinant strain K. oxytoca PDL-K5 was constructed. Fedbatch fermentation using K. oxytoca PDL-K5 produced 74.9 g/L BDO with a productivity of 2.27 g/L/h and a yield of 0.43 g/g from lactose. In addition, when whey powder was used as the substrate, 65.5 g/L BDO was produced within 24 h with a productivity of 2.73 g/L/h and a yield of 0.44 g/g. Conclusion: This study demonstrated the efficiency of K. oxytoca PDL-0 for BDO production from whey. Due to its non-pathogenicity and efficient lactose utilization, K. oxytoca PDL-0 might also be used in the production of other important chemicals using whey as the substrate.
Background: Transcatheter arterial chemoembolization (TACE), radiofrequency ablation (RFA), and microwave ablation (MWA) are regarded as effective therapies for treating unresectable hepatocellular carcinoma (HCC). We conducted this study to compare the efficiency and safety of TACE combined with RFA (TR group) or MWA (TM group).
Overflow metabolism-caused acetate accumulation is a major problem that restricts industrial applications of various bacteria. 2,3-Butanediol (2,3-BD) synthesis in microorganisms is an ancient metabolic process with unidentified functions. We demonstrate here that acetate increases and then decreases during the growth of a bacterium Enterobacter cloacae subsp. dissolvens SDM. Both bifunctional acetaldehyde/ethanol dehydrogenase AdhE-catalyzed ethanol production and acetate-induced 2,3-BD biosynthesis are indispensable for the elimination of acetate generated during overflow metabolism. 2,3-BD biosynthesis from glucose supplies NADH required for acetate elimination via AdhE-catalyzed ethanol production. The coupling strategy involving 2,3-BD biosynthesis and ethanol production is widely distributed in bacteria and is important for toxic acetate elimination. Finally, we realized the co-production of ethanol and acetoin from chitin, the second most abundant natural biopolymer whose catabolism involves inevitable acetate production through the coupling acetate elimination strategy. The synthesis of a non-toxic chemical such as 2,3-BD may be viewed as a unique overflow metabolism with desirable metabolic functions.
Acetoin is a potential platform compound for a variety of chemicals. Bacillus licheniformis MW3, a thermophilic and generally regarded as safe (GRAS) microorganism, can produce 2,3-butanediol with a high concentration, yield, and productivity. In this study, B. licheniformis MW3 was metabolic engineered for acetoin production. After deleting two 2,3-butanediol dehydrogenases encoding genes budC and gdh, an engineered strain B. licheniformis MW3 (budC gdh) was constructed. Using fedbatch fermentation of B. licheniformis MW3 (budC gdh), 64.2 g/L acetoin was produced at a productivity of 2.378 g/[L h] and a yield of 0.412 g/g from 156 g/L glucose in 27 h. The fermentation process exhibited rather high productivity and yield of acetoin, indicating that B. licheniformis MW3 (budC gdh) might be a promising acetoin producer.
BackgroundWhole cells of Gluconobacter oxydans are widely used in various biocatalytic processes. Sorbitol at high concentrations is commonly used in complex media to prepare biocatalysts. Exploiting an alternative process for preparation of biocatalysts with low cost substrates is of importance for industrial applications.Results G. oxydans 621H was confirmed to have the ability to grow in mineral salts medium with glycerol, an inevitable waste generated from industry of biofuels, as the sole carbon source. Based on the glycerol utilization mechanism elucidated in this study, the major polyol dehydrogenase (GOX0854) and the membrane-bound alcohol dehydrogenase (GOX1068) can competitively utilize glycerol but play no obvious roles in the biocatalyst preparation. Thus, the genes related to these two enzymes were deleted. Whole cells of G. oxydans ∆GOX1068∆GOX0854 can be prepared from glycerol with a 2.4-fold higher biomass yield than that of G. oxydans 621H. Using whole cells of G. oxydans ∆GOX1068∆GOX0854 as the biocatalyst, 61.6 g L−1 xylonate was produced from 58.4 g L−1 xylose at a yield of 1.05 g g−1.ConclusionThis process is an example of efficient preparation of whole cells of G. oxydans with reduced cost. Besides xylonate production from xylose, other biocatalytic processes might also be developed using whole cells of metabolic engineered G. oxydans prepared from glycerol.Electronic supplementary materialThe online version of this article (10.1186/s12934-018-1001-0) contains supplementary material, which is available to authorized users.
Pyruvate is an important platform material widely used in food, pharmaceutical, and chemical industries. Pyruvatetolerant Klebsiella oxytoca PDL-0 was chosen as a chassis for pyruvate production via metabolic engineering. Genes related to byproduct generation were knocked out to decrease the production of 2,3-butantediol, acetate, ethanol, and succinate. The NADH oxidase encoding gene nox was inserted into the locus of the lactate dehydrogenase encoding gene ldhD in the genome of K. oxytoca to simultaneously block lactate production and regenerate NAD + . The pyruvate importers CstA and YjiY were identified, and their encoding genes were deleted to increase pyruvate accumulation. The engineered strain K. oxytoca PDL-YC produced 71.0 g/L pyruvate from glucose. Furthermore, K. oxytoca PDL-YC can use whey powder, an abundant by-product of the cheese making process, as substrate for pyruvate production. Pyruvate production with a concentration of 62.3 g/L and a productivity of 1.60 g/[L• h] was realized using whey powder as substrate.
Background: Whey is a major pollutant generated by the dairy industry. To decrease environmental pollution caused by the industrial release of whey, new prospects for its utilization need to be urgently explored. Here, we investigated the possibility of using whey powder to produce 2,3-butanediol (BDO), an important platform chemical. Results: Klebsiella oxytoca strain PDL-0 was selected because of its ability to efficiently produce BDO from lactose, the major fermentable sugar in whey. After deleting genes pox , pta , frdA , ldhD , and pflB responding for the production of by-products acetate, succinate, lactate, and formate, a recombinant strain K. oxytoca PDL-K5 was constructed. Fed-batch fermentation using K. oxytoca PDL-K5 produced 74.9 g/L BDO with a productivity of 2.27 g/L/h and a yield of 0.43 g/g from lactose. In addition, when whey powder was used as the substrate, 65.5 g/L BDO was produced within 24 h with a productivity of 2.73 g/L/h and a yield of 0.44 g/g. Conclusion: This study demonstrated the efficiency of K. oxytoca PDL-0 for BDO production from whey. Due to its non-pathogenicity and efficient lactose utilization, K. oxytoca PDL-0 might also be used in the production of other important chemicals using whey as the substrate.
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