Sulfide oxidation by gene expressions of sulfide-quinone oxidoreductase and ubiquinone-8 biosynthase in Escherichia coli

Sulfides (S2),SH-) such as hydrogen sulfide belong to a class of sulfur compounds with unpleasant odors. In order to confer sulfide-oxidizing ability on the intestine-inhabiting bacteria, the sulfide-quinone oxidoreductase gene (sqr) in Rhodobacter capsulatus DSM-155 and genes for quinone biosynthesis (ubiC, ubiA and ispB) in Escherichia coli XL1 Blue-MRF' were transduced into E. coli BL21(DE3). Plasmids pT7-7 and pSTV were used as vectors of sqr, and ubiCA and ispB, respectively. The recombinants sqr-BL21(DE3) and ubiCA,ispB-sqr-BL21(DE3) were successfully constructed. The maximal sulfide-removing activities of the whole cells and membrane fractions of sqr-BL21(DE3) attained at pH 8.0 and 7.8, were 267 nmol/mg cells (dry weight)/min and 1250 nmol/mg membrane fraction (protein)/min, respectively. The molecular ratio of sulfide (S2-) oxidized and oxygen (O2) consumed was 2:1. SQR activity in the recombinant cells was positively restricted under anaerobic conditions and also by the addition of electron transfer inhibitors. Ubiquinone-8 (UQ-8) biosynthesis in the cells of ubiCA,ispB-sqr-BL21(DE3) increased as much as 2.2-fold compared with that of (pSTV)-sqr-BL21(DE3) during the 12-16 h incubation period. The maximal sulfide removal in the quinone-raised E. coli was attained slightly earlier, however, SQR activities thereafter were lower than those in (pSTV)-sqr-BL21(DE3).