BMC Genomics 2009, 10:165 http://www.biomedcentral.com/1471-2164/10/165 FEfifgeuctrseo3f deleting rpoS on GcvB-mediated acid resistance Effects of deleting rpoS on GcvB-mediated acid resistance. (A) Acid resistance in an rpoS mutant and an rpoS gcvB double mutant. (B) Effects of GcvB overproduction on acid resistance in an rpoS mutant. Cell cultures of E. coli MG1655 mutant strains were grown in LB broth (pH 7.0) at 37°C for 5 hrs and then acid challenged (pH 2.0) for 15 min. After neutralization by adding alkalinized LB (pH 9.3), cells were cultured for an additional 3 hrs before measurement of optical density at 600 nm (OD600 nm). Error bars represent standard deviation (* P-value < 0.05). is therefore unlikely that BarA is a potential target for GcvB. Consequently, we examined whether GcvB exerts its positive control of RpoS through Crp, H-NS or GadX. We found that deleting gcvB reduced acid survival levels in an hns mutant background. This was also the case for crp- or gadX-deficient strains (Fig. 5). Consistent with the knockout data, gcvB overexpression increased AR levels in the hns-, crp- or gadX-deficient strains (Fig. 6). These results suggest that Hns, Crp and GadX are not involved in the GcvB-mediated regulation of rpoS expression. rpoS transcription is driven by a major promoter rpoSp and two weak promoters nlpDp1 and 2 [26]. To examine whether GcvB affected rpoS expression at the transcrip- sEFifiofgenuctorsefoR4fpGoScviBn asncchRrNomAoasnodmOalprppAoSp-lraocZterinepoonrtehre setxrapirnes- Effects of GcvB sncRNA and OppA protein on the expression of RpoS in a chromosomal rpoS-lacZ reporter strain. (A) Effects of deleting gcvB on the expres- sion of an rpoS-lacZ reporter gene fusion in E. coli MG1655. (B) Effect of GcvB overproduction on the expression of the rpoS-lacZ fusion. GcvB production was driven by its native promoter on a pET32a plasmid construct. (C) Effect of delet- ing oppA on the expression of the rpoS-lacZ reporter. Beta- galactosidase activities due to translation of chromosomal lacZ fusions were normalized to those of MG1655 carrying an rpoS-lacZ fusion with or without an empty vector (con- trols). Error bars represent standard deviation (* P-value < 0.05). Page 4 of 7 (page number not for citation purposes)