Differential expression of NiFe uptake-type hydrogenase genes in Salmonella enterica serovar Typhimurium

Abstract

Salmonella enterica serovar Typhimurium possesses three similar NiFe hydrogenases important to its virulence. Here we show that the three hydrogenase operons hyb, hya and hyd are expressed under different environmental conditions and are subject to control by different regulatory proteins. Hydrogenase promoter-lacZ fusion plasmids were transferred into the wild-type strain or into arcA, fnr, iscR, narL and narP deletion mutants, or into a fnr/arcA double mutant. The hyb promoter had highest b-galactosidase activity under growth conditions promoting anaerobic respiration (glycerol plus fumarate) and may be subject to glucose repression, since cells grown with glucose had about half the transcriptional activity of cells grown with mannose. Based on the phenotype of regulatory mutant strains, IscR represses hyb aerobically, and ArcA plays a role in both hyb and hyd regulation. The hyd promoter had about five times more activity in cells grown under aerobic conditions compared to anaerobic levels, and its activity tripled in an arcA mutant grown anaerobically. The hya promoter had the highest activity when cells were grown anaerobically with glucose, and the growth yield of the hya mutant was about 25 % lower than for wild-type cells grown fermentatively, suggesting that Hya may be utilized during fermentation. The hya promoter is repressed by nitrate and this repression was abolished when the NarL-binding site was mutated, or in a narL mutant background. FNR is involved in hyb and hya regulation, since b-galactosidase activity decreased significantly in a fnr mutant. These findings suggest that the three hydrogenases are used under different conditions, likely enhancing the pathogen's capacity to survive in a variety of environments.

Lag Phase Is a Distinct Growth Phase That Prepares Bacteria for Exponential Growth and Involves Transient Metal Accumulation

“…7) (52,53,96). Nickel has a biological role as a cofactor for anaerobically expressed NiFe hydrogenases (76,121). Like molybdenum, the gradual removal of cell-associated nickel and cobalt coincided with an oxygen upshift during lag phase.…”

Thiosulfate Reduction in Salmonella enterica Is Driven by the Proton Motive Force

“…The dashed box around thiosulfate reductase indicates that this enzyme is present only in S. enterica but can be functionally expressed in E. coli as in this work. S. enterica possesses an additional hydrogen:quinone oxidase reductase that is homologous to HYD-1 but expressed under aerobic conditions and not depicted here (81). UQ, ubiquinone; DMK, demethylmenaquinone; MK, menaquinone; DMSO, dimethyl sulfoxide; TMAO, trimethylamine N-oxide.…”

ArcA and AppY Antagonize IscR Repression of Hydrogenase-1 Expression under Anaerobic Conditions, Revealing a Novel Mode of O 2 Regulation of Gene Expression in Escherichia coli

“…Surprisingly, the mechanism of O 2 regulation of P hyaA described here for E. coli K-12 is not conserved in the close relative Salmonella enterica serovar Typhimurium. Rather, hya expression in S. enterica is regulated not by IscR or ArcA but, rather, by FNR under anaerobic conditions (38). However, comparison of the hyaA upstream promoter regions from the two organisms suggests that while the IscR binding site is conserved, a single base pair mismatch to the ArcA site may decrease DNA binding, thus preventing ArcA regulation (Fig.…”