Alternative sigma factor interactions in Salmonella: sigma and sigma promote antioxidant defences by enhancing sigma levels.
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), sigma(E) responds to extracytoplasmic stress, whereas sigma(H) responds to heat shock and sigma(S) is induced during nutrient limitation. Deficiency of sigma(E), sigma(H) or sigma(S) increases S. Typhimurium susceptibility to oxidative stress, but an analysis of double and triple mutants suggested that antioxidant actions of sigma(E) and sigma(H) might be dependent on sigma(S). Transcriptional profiling of mutant Salmonella lacking sigma(E) revealed reduced expression of genes dependent on sigma(H) and sigma(S) in addition to sigma(E). Further investigation demonstrated that sigma(E) augments sigma(S) levels during stationary phase via enhanced expression of sigma(H) and the RNA-binding protein Hfq, leading to increased expression of sigma(S)-dependent genes and enhanced resistance to oxidative stress. Maximal expression of the sigma(S)-regulated gene katE required sigma(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.
Bang
Iel-Soo
IS
Department of Laboratory Medicine, University of Washington School of Medicine, Seattle, WA 98195, USA.
Frye
Jonathan G
JG
McClelland
Michael
M
Velayudhan
Jyoti
J
Fang
Ferric C
FC
D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D035001:Host Factor 1 Protein / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress; D011401:Promoter Regions, Genetic; D025941:Protein Interaction Mapping; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D000975:Antioxidants; D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D035001:Host Factor 1 Protein; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C069567:sigma factor KatF protein, Bacteria; C063202:sporulation-specific sigma factors; C102664:hydroperoxidase II; D002374:Catalase