The rpoS-dependent starvation-stress response locus stiA encodes a nitrate reductase (narZYWV) required for carbon-starvation-inducible thermotolerance and acid tolerance in Salmonella typhimurium.
The starvation-stress response (SSR) of Salmonella typhimurium includes gene products necessary for starvation avoidance, starvation survival and virulence for this bacterium. Numerous genetic loci induced during carbon-source starvation and required for the long-term-starvation survival of this bacterium have been identified. The SSR not only protects the cell against the adverse effects of long-term starvation but also provides cross-resistance to other environmental stresses, e.g. thermal challenge (55 degrees C) or acid-pH challenge (pH 2.8). One carbon-starvation-inducible lac fusion, designated stiA was previously reported to be a sigma(S)-dependent SSR locus that is phosphate-starvation, nitrogen-starvation and H2O2 inducible, positively regulated by (p)ppGpp in a relA-dependent manner, and negatively regulated by cAMP:cAMP receptor protein complex and OxyR. We have discovered through sequence analysis and subsequent biochemical analysis that the stiA::lac fusion, and a similarly regulated lac fusion designated sti-99, lie at separate sites within the first gene (narZ) of an operon encoding a cryptic nitrate reductase (narZYWV) of unknown physiological function. In this study, it was demonstrated that narZ was negatively regulated by the global regulator Fnr during anaerobiosis. Interestingly, narZ(YWV) was required for carbon-starvation-inducible thermotolerance and acid tolerance. In addition, narZ expression was induced approximately 20-fold intracellularly in Madin-Darby canine kidney epithelial cells and 16-fold in intracellular salts medium, which is believed to mimic the intracellular milieu. Also, a narZ1 knock-out mutation increased the LD50 approximately 10-fold for S. typhimurium SL1344 delivered orally in the mouse virulence model. Thus, the previously believed cryptic and constitutive narZYWV operon is in fact highly regulated by a complex network of environmental-stress signals and global regulatory functions, indicating a central role in the physiology of starved and stressed cells.
Spector
Michael P
MP
Department of Biomedical Sciences1 and Department of Microbiology and Immunology2, University of South Alabama, Mobile, AL 36688, USA.
Garcia Del Portillo
Francisco
F
Biotechnology Laboratory and Departments of Biochemistry and Microbiology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z33.
Bearson
Shawn M D
SMD
Department of Biomedical Sciences1 and Department of Microbiology and Immunology2, University of South Alabama, Mobile, AL 36688, USA.
Mahmud
Atif
A
Department of Biomedical Sciences1 and Department of Microbiology and Immunology2, University of South Alabama, Mobile, AL 36688, USA.
Magut
Maureen
M
Department of Biomedical Sciences1 and Department of Microbiology and Immunology2, University of South Alabama, Mobile, AL 36688, USA.
Finlay
B Brett
BB
Biotechnology Laboratory and Departments of Biochemistry and Microbiology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z33.
Dougan
Gordon
G
Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY, UK4.
Foster
John W
JW
Department of Biomedical Sciences1 and Department of Microbiology and Immunology2, University of South Alabama, Mobile, AL 36688, USA.
Pallen
Mark J
MJ
Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY, UK4.
D000595:Amino Acid Sequence; D000818:Animals; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D003470:Culture Media / Q000737:chemistry; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D005809:Genes, Regulator; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000235:genetics; D007763:Lac Operon / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000472:pathogenicity / Q000502:physiology*; D012808:Sigma Factor; D013696:Temperature; D014774:Virulence
D001426:Bacterial Proteins; D003470:Culture Media; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D012808:Sigma Factor; D009565:Nitrate Reductases; D050901:Nitrate Reductase