, 2010), and this could have an impact on these viable cell numbers. In contrast, disruption of sciP resulted in a significant decrease in viable cells in the stationary phase. Neither of these mutant strains was affected for growth rate or culture turbidity. This is the first instance where

loss of an R. capsulatus homolog of a member of the C. crescentus CtrA network negatively affects cell viability. The reasons for these changes in stationary phase viable cell numbers remain to be determined. Our data support the involvement of CckA, ChpT, and SciP in a regulatory system related to CtrA function in R. capsulatus (Fig. 5). SciP function as a negative regulator of motility is conserved TSA HDAC between R. capsulatus and C. crescentus. Our data does not allow us to conclude there is a phosphorelay from CckA-ChpT to CtrA, but there is clear co-involvement of these proteins in the regulation of motility and RcGTA release. The reduction, but not complete loss, of motility and RcGTA gene transfer activity in the cckA and chpT strains could also reflect alternative sources for CtrA phosphorylation. RcGTA release, but not gene expression, is dependent on CtrA phosphorylation.

Although it is CtrA~P that binds many regulatory sequences in C. crescentus (Reisenauer et al., 1999; Siam & Marczynski, 2000), the unphosphorylated protein is also active (Spencer et al., 2009), and other response regulators have been shown to both activate and repress a variety of genes CX 5461 in unphosphorylated forms, including RegA in R. capsulatus (Bird et al., 1999). There are no predicted CtrA-binding sites upstream of either the motility or RcGTA genes (Lang & Beatty, 2000; Mercer et al., 2010), which presumably reflects indirect control new of transcription initiation of these genes by CtrA. We thank S. Christian

for help with statistical tests. R.M. was supported by fellowships from the Memorial University School of Graduate Studies and the Natural Sciences and Engineering Research Council (NSERC) of Canada. M.Q. was supported in part by the Biology Department Honours program. J.T.B.’s research is supported by a grant from the Canadian Institutes of Health Research. This work in A.S.L.’s laboratory was supported by a grant from NSERC. “
“Department of Microbiology, Cornell University, Ithaca, NY, USA In Salmonella enterica serovar Typhimurium, proteolytic cleavage of the membrane-bound transcriptional regulator CadC acts as a switch to activate genes of the lysine decarboxylase system in response to low pH and lysine signals. To identify the genetic factors required for the proteolytic activation of CadC, we performed genome-wide random mutagenesis. We show that a phosphotransferase system (PTS) permease STM4538 acts as a positive modulator of CadC function. The transposon insertion in STM4538 reduces the expression of the CadC target operon cadBA under permissive conditions.