• Korean Journal of Microbiology
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• v.55 no.1
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• pp.9-16
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• 2019

Acetoin is generated by numerous microorganisms using ${\alpha}$-acetolactate decarboxylase (ALDC) to prevent overacidification of cells and their environment and to store remaining energy. Because acetoin has been used as a safe flavor enhancer in food products, industries have been interested in biotechnological production of acetoin using ALDC. ALDC is a metal-dependent enzyme that produces acetoin from ${\alpha}$-acetolactate through decarboxylation reaction. Here, we report the crystal structure of ALDC from Bacillus subtilis subspecies spizizenii (bssALDC) at $1.7{\AA}$ resolution. bssALDC folds into a two-domain ${\alpha}/{\beta}$ structure where two ${\beta}$-sheets form a central core. bssALDC assembles into a dimer through central hydrophobic interactions and peripheral hydrophilic interactions. bssALDC coordinates a zinc ion using three histidine residues and three water molecules. Based on comparative analyses of ALDC structures and sequences, we propose that the active site of bssALDC includes the zinc ion and its neighboring bssALDC residues.

• Journal of Microbiology and Biotechnology
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• v.22 no.9
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• pp.1258-1263
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• 2012

2,3-Butanediol (2,3-BD) is a major metabolite produced by Klebsiella pneumoniae KCTC2242, which is a important chemical with wide applications. Three genes important for 2,3-BD biosynthesis acetolactate decarboxylase (budA), acetolactate synthase (budB), and alcohol dehydrogenase (budC) were identified in K. pneumoniae genomic DNA. With the goal of enhancing 2,3-BD production, these genes were cloned into pUC18K expression vectors containing the lacZ promoter and the kanamycin resistance gene to generate plasmids pSB1-7. The plasmids were then introduced into K. pneumoniae using electroporation. All strains were incubated in flask experiments and 2,3-BD production was increased by 60% in recombinant bacteria harboring pSB04 (budA and budB genes), compared with the parental strain K. pneumoniae KCTC2242. The maximum 2,3-BD production level achieved through fed-batch fermentation with K. pneumoniae SGJSB04 was 101.53 g/l over 40 h with a productivity of 2.54 g/l.h. These results suggest that overexpression of 2,3-BD synthesis-related genes can enhance 2,3-BD production in K. pneumoniae by fermentation.

• Journal of Microbiology and Biotechnology
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• v.29 no.4
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• pp.596-606
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• 2019

N-acyl-homoserine lactone quorum sensing (AHL-QS) has been shown to regulate many physiological behaviors in Serratia marcescens MG1. In the current study, the effects of AHL-QS on the biosynthesis of acid and neutral products by S. marcescens MG1 and its isogenic ${\Delta}swrI$ with or without supplementing exogenous N-hexanoyl-L-homoserine lactone ($C_6-HSL$) were systematically investigated. The results showed that swrI disruption resulted in rapid pH drops from 7.0 to 4.8, which could be restored to wild type by supplementing $C_6-HSL$. Furthermore, fermentation product analysis indicated that ${\Delta}swrI$ could lead to obvious accumulation for acidogenesis products such as lactic acid and succinic acid, especially excess acetic acid (2.27 g/l) produced at the early stage of fermentation, whereas solventogenesis products by ${\Delta}swrI$ appeared to noticeably decrease by an approximate 30% for acetoin during 32-48 h and by an approximate 20% for 2,3-butanediol during 24-40 h, when compared to those by wild type. Interestingly, the excess acetic acid produced could be removed in an AHL-QS-independent manner. Subsequently, quantitative real-time PCR was used to determine the mRNA expression levels of genes responsible for acidogenesis and solventogenesis and showed consistent results with those of product synthesis. Finally, by close examination of promoter regions of the analyzed genes, four putative luxI box-like motifs were found upstream of genes encoding acetyl-CoA synthase, lactate dehydrogenase, ${\alpha}$-acetolactate decarboxylase, and Lys-like regulator. The information from this study provides a novel insight into the roles played by AHL-QS in switching from acidogenesis to solventogenesis in S. marcescens MG1.