A. Morton for critical review of the manuscript and E. Diakun for technical assistance. C.J. and R.Y. were supported by NSERC scholarships.

Electronic supplementary material Additional file 1: Alignment of rpoS gene sequences of Suc ++ mutants with parental strains. The alignment data show the location of mutations within the rpoS gene in the selected Suc++ mutants in comparison with parental strains. (PDF 349 KB) Additional file 2: Alignment of predicted RpoS protein sequences of Suc ++ mutants with parental strains. The protein alignment MK-4827 data show the predicted mutant forms of RpoS resulting from the identified mutations in the rpoS gene of Suc++ mutants. (PDF 128 KB) References 1. Stoodley P, Sauer K, Davies DG, Costerton JW: Biofilms as complex differentiated communities. Annu Rev Microbiol 2002, 56:187–209.CrossRefPubMed 2. Davidson CJ, Surette MG: Individuality in bacteria. Annu Rev Genet 2008, 42:253–268.CrossRefPubMed 3. Wolf DM, Vazirani VV, Arkin AP: Diversity in times of adversity: probabilistic strategies in microbial survival games. J Theor Biol 2005, 234:227–253.CrossRefPubMed 4. Lederberg J, Iino T: Phase Variation in Salmonella.

Genetics 1956, 41:743–757.PubMed 5. Hallet B: Playing Dr Jekyll and Mr Hyde: combined mechanisms of phase variation in bacteria. Curr Opin Microbiol 2001, 4:570–581.CrossRefPubMed 6. Tolker-Nielsen T, Holmstrom K, Boe L, Molin S: Non-genetic population heterogeneity studied by in situ polymerase chain reaction. Mol Microbiol 1998, 27:1099–1105.CrossRefPubMed 7. Ozbudak EM, Thattai M, Kurtser I, Grossman MK-1775 mouse AD, van Oudenaarden A: Regulation

of noise in the expression of a single gene. Nat Genet 2002, 31:69–73.CrossRefPubMed Bacterial neuraminidase 8. Dong T, Joyce C, Schellhorn HE: The Role of RpoS in Bacterial Adaptation. Bacterial Physiology – A Molecular Approach (Edited by: Walid M El-Sharoud). Springer, Berlin, Germany 2008, 313–337. 9. Hengge-Aronis R: The general stress response in Escherichia coli. Bacterial stress response (Edited by: Storz G, Hengge-Aronis R). Washington, D.C.: ASM press 2000, 161–178. 10. Dong T, Kirchhof MG, Schellhorn HE: RpoS regulation of gene expression during exponential growth of Escherichia coli K12. Mol Genet Genomics 2008, 279:267–277.CrossRefPubMed 11. RAD001 Lacour S, Landini P: SigmaS-dependent gene expression at the onset of stationary phase in Escherichia coli : function of sigmaS-dependent genes and identification of their promoter sequences. J Bacteriol 2004, 186:7186–7195.CrossRefPubMed 12. Patten CL, Kirchhof MG, Schertzberg MR, Morton RA, Schellhorn HE: Microarray analysis of RpoS-mediated gene expression in Escherichia coli K-12. Mol Genet Genomics 2004, 272:580–591.CrossRefPubMed 13. Weber H, Polen T, Heuveling J, Wendisch VF, Hengge R: Genome-wide analysis of the general stress response network in Escherichia coli : sigmaS-dependent genes, promoters, and sigma factor selectivity. J Bacteriol 2005, 187:1591–1603.CrossRefPubMed 14.