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^s-Dependent carbon-starvation induction of pbpG (PBP 7) is required for the starvation-stress response in Salmonella enterica serovar Typhimurium

William J. Kenyon^1,

¹ Department of Biomedical Sciences, University of South Alabama, Mobile, AL 36688, USA
² Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 845 51 Bratislava 45, Slovak Republic
³ Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-CSIC, C/ Darwin 3, 28049 Madrid, Spain
⁴ The University of British Columbia, Michael Smith Laboratories, 301-2185 East Mall, Vancouver, BC, Canada V6T 1Z4
⁵ Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham B15 2TT, UK

Correspondence
Michael P. Spector
mspector{at}usouthal.edu

Carbon-energy source starvation is a commonly encountered stress that can influence the epidemiology and virulence of Salmonella enterica serovars. Salmonella responds to C-starvation by eliciting the starvation-stress response (SSR), which allows for long-term C-starvation survival and cross-resistance to other stresses. The stiC locus was identified as a C-starvation-inducible, ^S-dependent locus required for a maximal SSR. We report here that the stiC locus is an operon composed of the yohC (putative transport protein) and pbpG (penicillin-binding protein-7/8) genes. yohC pbpG transcription is initiated from a ^S–dependent C-starvation-inducible promoter upstream of yohC. Another (^S-independent) promoter, upstream of pbpG, drives lower constitutive pbpG transcription, primarily during exponential phase. C-starvation-inducible pbpG expression was required for development of the SSR in 5 h, but not 24 h, C-starved cells; yohC was dispensable for the SSR. Furthermore, the yohC pbpG operon is induced within MDCK epithelial cells, but was not essential for oral virulence in BALB/c mice. Thus, PBP 7 is required for physiological changes, occurring within the first few hours of C-starvation, essential for the development of the SSR. Lack of PBP 7, however, can be compensated for by further physiological changes developed in 24 h C-starved cells. This supports the dynamic overlapping and distinct nature of resistance pathways within the Salmonella SSR.

Present address: Department of Biology, University of West Georgia, Carrollton, GA 30118, USA

Alignments of YohC proteins and phylogenetic tree are available with the online version of this paper.