Novel (2R,3R)-2,3-butanediol dehydrogenase from potential industrial strain Paenibacillus polymyxa ATCC 12321

A newly isolated Bacillus licheniformis strain thermophilically produces 2,3-butanediol, a platform and fuel bio-chemical

BACKGROUND

2,3-Butanediol (2,3-BD), a platform and fuel bio-chemical, can be efficiently produced by Klebsiella pneumonia, K. oxytoca, and Serratia marcescens. However, these strains are opportunistic pathogens and not favorable for industrial application. Although some generally regarded as safe (GRAS) microorganisms have been isolated in recent years, there is still a demand for safe 2,3-BD producing strains with high productivity and yield under thermophilic fermentation.

RESULTS

Bacillus licheniformis strain 10-1-A was newly isolated for 2,3-BD production. The optimum temperature and medium pH were 50°C and pH 7.0 for 2,3-BD production by strain 10-1-A. The medium composition was optimized through Plackett-Burman design and response surface methodology techniques. With a two-stage agitation speed control strategy, 115.7 g/L of 2,3-BD was obtained from glucose by fed-batch fermentation in a 5-L bioreactor with a high productivity (2.4 g/L·h) and yield (94% of its theoretical value). The 2,3-BD produced by strain 10-1-A comprises (2R,3R)-2,3-BD and meso-2,3-BD with a ratio of nearly 1:1. The bdh and gdh genes encoding meso-2,3-butanediol dehydrogenase (meso-BDH) and glycerol dehydrogenase (GDH) of strain 10-1-A were expressed in Escherichia coli and the proteins were purified. meso-2,3-BD and (2R,3R)-2,3-BD were transformed from racemic acetoin by meso-BDH and GDH with NADH, respectively.

CONCLUSIONS

Compared with the reported GRAS 2,3-BD producers, B. licheniformis 10-1-A could thermophilically produce 2,3-BD with a high concentration, productivity and yield. Thus, the newly isolated GRAS strain 10-1-A might be a promising strain for industrial production of 2,3-BD. Two key enzymes for meso-2,3-BD and (2R,3R)-2,3-BD production were purified and further studied, and this might be helpful to understand the mechanism for 2,3-BD stereoisomers forming in B. licheniformis.

Genome Sequence of Paenibacillus polymyxa ATCC 12321, a Promising Strain for Optically Active (R,R)-2,3-Butanediol Production

Paenibacillus polymyxa is a potential strain for (R,R)-2,3-butanediol production. Here, we report an annotated draft genome sequence of P. polymyxa strain ATCC 12321, which contains 4,429 protein-coding genes and 49 structural RNAs. This genome sequence provides a genetic basis for a better understanding of the mechanism for the accumulation of highly optically active (R,R)-2,3-butanediol.

Production of S-acetoin from diacetyl by Escherichia coli transformant cells that express the diacetyl reductase gene of Paenibacillus polymyxa ZJ-9

S-acetoin (S-AC) is an important four-carbon chiral compound that has unique industrial applications in the asymmetric synthesis of valuable chiral specialty chemicals. However, previous studies showed that the usually low yield and optical purity of S-AC as well as the very high substrate cost have hindered the application of this compound. In the current work, a gene encoding diacetyl reductase (DAR) from a Paenibacillus polymyxa strain ZJ-9 was cloned and expressed in Escherichia coli. Whole cells of the recombinant E. coli were used to produce S-AC from diacetyl (DA). Under optimal conditions, S-AC with high optical purity (purity >99·9%) was obtained with a yield of 13·5 ± 0·24 and 39·4 ± 0·38 g l(-1) under batch and fed-batch culture conditions, respectively. This process featured the biotransformation of DA into S-AC using whole cells of engineered E. coli. The result is a considerable increase in the yield and optical purity of S-AC, which in turn facilitated the practical application of the compound.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated a highly efficient new method to produce S-acetoin with higher than 99·9% optical purity from diacetyl using whole cells of engineered Escherichia coli. It will therefore decrease the production cost of S-acetoin and highlight its application in asymmetric synthesis of highly valuable chiral compounds.

A new NAD(H)-dependent meso-2,3-butanediol dehydrogenase from an industrially potential strain Serratia marcescens H30

The budC gene coding for a new meso-2,3-butanediol dehydrogenase (BDH) from Serratia marcescens H30 was cloned and expressed in Escherichia coli BL21(DE3), purified, and characterized for its properties. The recombinant BDH with a molecular weight of 27.4 kDa exhibited a reversible transformation between acetoin and 2,3-butanediol. In the presence of NADH, BDH could catalyze the reduction of diacetyl and (3R)-acetoin to (3S)-acetoin and meso-2,3-butanediol, respectively, while (3S)-acetoin as a substrate could be further transformed into (2S, 3S)-2,3-butanediol at pH 9.0. For diol oxidation reactions, (3R)-acetoin and (3S)-acetoin were obtained when meso-2,3-butanediol and (2S,3S)-2,3-butanediol were used as the substrates with BDH and NAD(+). (2R,3R)-2,3-butanediol was not a substrate for the BDH at all. The low K m value (4.1 mM) in meso-2,3-butanediol oxidation reaction and no activity for diacetyl, acetoin, and 2,3-butanediol as the substrates with NADP(+)/NADPH suggested that the budC gene product belongs to a NAD(H)-dependent meso-2,3-BDH. Maximum activities for diacetyl and (3S/3R)-acetoin reduction were observed at pH 8.0 and pH 5.0 while for meso-2,3-butanediol oxidation it was pH 8.0. However, the optimum temperature for oxidation and reduction reactions was about 40 °C. In addition, the BDH activity for meso-2,3-butanediol oxidation was enhanced in the presence of Fe(2+) and for diacetyl and (3S/3R)-acetoin reduction in the presence of Mg(2+) and Mn(2+), while several metal ions inhibited its activity, particularly Fe(3+) for reduction of diacetyl and acetoin. Sequence analysis showed that the BDH from S. marcescens H30 possessed two conserved sequences including the coenzyme binding motif (GxxxGxG) and the active-site motif (YxxxK), which are present in the short-chain dehydrogenase/reductase superfamily.

The genome of Pelobacter carbinolicus reveals surprising metabolic capabilities and physiological features

Background

The bacterium Pelobacter carbinolicus is able to grow by fermentation, syntrophic hydrogen/formate transfer, or electron transfer to sulfur from short-chain alcohols, hydrogen or formate; it does not oxidize acetate and is not known to ferment any sugars or grow autotrophically. The genome of P. carbinolicus was sequenced in order to understand its metabolic capabilities and physiological features in comparison with its relatives, acetate-oxidizing Geobacter species.

Results

Pathways were predicted for catabolism of known substrates: 2,3-butanediol, acetoin, glycerol, 1,2-ethanediol, ethanolamine, choline and ethanol. Multiple isozymes of 2,3-butanediol dehydrogenase, ATP synthase and [FeFe]-hydrogenase were differentiated and assigned roles according to their structural properties and genomic contexts. The absence of asparagine synthetase and the presence of a mutant tRNA for asparagine encoded among RNA-active enzymes suggest that P. carbinolicus may make asparaginyl-tRNA in a novel way. Catabolic glutamate dehydrogenases were discovered, implying that the tricarboxylic acid (TCA) cycle can function catabolically. A phosphotransferase system for uptake of sugars was discovered, along with enzymes that function in 2,3-butanediol production. Pyruvate:ferredoxin/flavodoxin oxidoreductase was identified as a potential bottleneck in both the supply of oxaloacetate for oxidation of acetate by the TCA cycle and the connection of glycolysis to production of ethanol. The P. carbinolicus genome was found to encode autotransporters and various appendages, including three proteins with similarity to the geopilin of electroconductive nanowires.

Conclusions

Several surprising metabolic capabilities and physiological features were predicted from the genome of P. carbinolicus, suggesting that it is more versatile than anticipated.

Thermophilic fermentation of acetoin and 2,3-butanediol by a novel Geobacillus strain

BACKGROUND

Acetoin and 2,3-butanediol are two important biorefinery platform chemicals. They are currently fermented below 40°C using mesophilic strains, but the processes often suffer from bacterial contamination.

RESULTS

This work reports the isolation and identification of a novel aerobic Geobacillus strain XT15 capable of producing both of these chemicals under elevated temperatures, thus reducing the risk of bacterial contamination. The optimum growth temperature was found to be between 45 and 55°C and the medium initial pH to be 8.0. In addition to glucose, galactose, mannitol, arabionose, and xylose were all acceptable substrates, enabling the potential use of cellulosic biomass as the feedstock. XT15 preferred organic nitrogen sources including corn steep liquor powder, a cheap by-product from corn wet-milling. At 55°C, 7.7 g/L of acetoin and 14.5 g/L of 2,3-butanediol could be obtained using corn steep liquor powder as a nitrogen source. Thirteen volatile products from the cultivation broth of XT15 were identified by gas chromatography-mass spectrometry. Acetoin, 2,3-butanediol, and their derivatives including a novel metabolite 2,3-dihydroxy-3-methylheptan-4-one, accounted for a total of about 96% of all the volatile products. In contrast, organic acids and other products were minor by-products. α-Acetolactate decarboxylase and acetoin:2,6-dichlorophenolindophenol oxidoreductase in XT15, the two key enzymes in acetoin metabolic pathway, were found to be both moderately thermophilic with the identical optimum temperature of 45°C.

CONCLUSIONS

Geobacillus sp. XT15 is the first naturally occurring thermophile excreting acetoin and/or 2,3-butanediol. This work has demonstrated the attractive prospect of developing it as an industrial strain in the thermophilic fermentation of acetoin and 2,3-butanediol with improved anti-contamination performance. The novel metabolites and enzymes identified in XT15 also indicated its strong promise as a precious biological resource. Thermophilic fermentation also offers great prospect for improving its yields and efficiencies. This remains a core aim for future work.

Production of (2S,3S)-2,3-butanediol and (3S)-acetoin from glucose using resting cells of Klebsiella pneumonia and Bacillus subtilis

Production of highly pure (2S,3S)-2,3-butanediol ((2S,3S)-2,3-BD) and (3S)-acetoin ((3S)-AC) in high concentrations is desirable but difficult to achieve. In the present study, glucose was first transformed to a mixture of (2S,3S)-2,3-BD and meso-2,3-BD by resting cells of Klebsiella pneumoniae CICC 10011, followed by biocatalytic resolution of the mixture by resting cells of Bacillus subtilis 168. meso-2,3-BD was transformed to (3S)-AC, leaving (2S,3S)-2,3-BD in the reaction medium. Using this approach, 12.5 g l(-1) (2S,3S)-2,3-BD and 56.7 g l(-1) (3S)-AC were produced. Stereoisomeric purity of (2S,3S)-2,3-BD and enantiomeric excess of (3S)-AC was 96.9 and 96.2%, respectively.

Fuels and chemicals from hemicellulose sugars

Industrial processes of lignocellulosic material have made use of only the hexose component of the cellulose fraction. Pentoses and some minor hexoses present in the hemicellulose fraction, which may represent as much as 40% of lignocellulosic biomass, have in most cases been wasted. The lack of good methods for utilization of hemicellulose sugars is a key obstacle hindering the development of lignocellulose-based ethanol and other biofuels. In this chapter, we focus on the utilization of hemicellulose sugars, the structure of hemicellulose and its hydrolysis, and the biochemistry and process technology involved in their conversion to valuable fuels and chemicals.