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Alternative sigma factor interactions in Salmonella : σ E and σ H promote antioxidant defences by enhancing σ S levels
Author(s) -
Bang IelSoo,
Frye Jonathan G.,
McClelland Michael,
Velayudhan Jyoti,
Fang Ferric C.
Publication year - 2005
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04580.x
Subject(s) - sigma factor , sigma , biology , mutant , gene expression , gene , salmonella , salmonella enterica , rpos , regulon , genetics , microbiology and biotechnology , bacteria , promoter , physics , quantum mechanics
Summary Hierarchical interactions between alternative sigma factors control sequential gene expression in Gram‐positive bacteria, whereas alternative sigma factors in Gram‐negative bacteria are generally regarded to direct expression of discrete gene subsets. In Salmonella enterica serovar Typhimurium ( S. Typhimurium), σ E responds to extracytoplasmic stress, whereas σ H responds to heat shock and σ S is induced during nutrient limitation. Deficiency of σ E , σ H or σ S increases S. Typhimurium susceptibility to oxidative stress, but an analysis of double and triple mutants suggested that antioxidant actions of σ E and σ H might be dependent on σ S . Transcriptional profiling of mutant Salmonella lacking σ E revealed reduced expression of genes dependent on σ H and σ S in addition to σ E . Further investigation demonstrated that σ E augments σ S levels during stationary phase via enhanced expression of σ H and the RNA‐binding protein Hfq, leading to increased expression of σ S ‐dependent genes and enhanced resistance to oxidative stress. Maximal expression of the σ S ‐regulated gene katE required σ E in Salmonella ‐infected macrophages as well as stationary‐phase cultures. Interactions between alternative sigma factors permit the integration of diverse stress signals to produce coordinated genetic responses.