Investigations into sigmaB-modulated regulatory pathways governing extracellular virulence determinant production in Staphylococcus aureus.
The commonly used Staphylococcus aureus laboratory strain 8325-4 bears a naturally occurring 11-bp deletion in the sigmaB-regulating phosphatase rsbU. We have previously published a report (M. J. Horsburgh, J. L. Aish, I. J. White, L. Shaw, J. K. Lithgow, and S. J. Foster, J. Bacteriol. 184:5457-5467, 2002) on restoring the rsbU deletion, producing a sigmaB-functional 8325-4 derivative, SH1000. SH1000 is pleiotropically altered in phenotype from 8325-4, displaying enhanced pigmentation, increased growth yields, and a marked decrease in secreted exoproteins. This reduction in exoprotein secretion appears to result from a sixfold reduction in agr expression. In this study we have undertaken transposon mutagenesis of SH1000 to identify components involved in the modulation of extracellular proteases and alpha-hemolysin compared to 8325-4. In total, 13 genes were identified displaying increased alpha-hemolysin transcription and extracellular proteolysis. Phenotypic analysis revealed that each mutant also had decreased pigmentation and a general increase in protein secretion. Interestingly this phenotype was not identical in each case but was variable from mutant to mutant. None of the genes identified encoded classic regulatory proteins but were predominantly metabolic enzymes involved in amino acid biosynthesis and transport. Further analysis revealed that all of these mutations were clustered in a 35-kb region of the chromosome. By complementation and genetic manipulation we were able to demonstrate the validity of these mutations. Interestingly transcriptional analysis revealed that rather than being regulated by sigmaB, these genes appeared to have a role in the regulation of sigmaB activity. Thus, we propose that the loss of individual genes in this chromosomal hot spot region results in a destabilization of cellular harmony and disruption of the sigmaB regulatory cascade.
Shaw
Lindsey N
LN
Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA. lesshaw@uga.edu
Aish
Joanne
J
Davenport
Jessica E
JE
Brown
Melanie C
MC
Lithgow
James K
JK
Simmonite
Kay
K
Crossley
Howard
H
Travis
James
J
Potempa
Jan
J
Foster
Simon J
SJ
D001426:Bacterial Proteins / Q000235:genetics*; D002876:Chromosomes, Bacterial / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics*; D006360:Heat-Shock Proteins / Q000235:genetics*; D006460:Hemolysin Proteins / Q000235:genetics; D005810:Multigene Family / Q000235:genetics; D010447:Peptide Hydrolases / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics*; D013211:Staphylococcus aureus / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; C079011:SigB protein, Bacteria; D012808:Sigma Factor; D010447:Peptide Hydrolases