The RcsCDB system activator signals are released into conditioned mediums of Salmonella enterica serovar Typhimurium

TERÁN, L; PESCARETTI MM,; FARIZANO JV; DELGADO, M. A.

Santos, San Pablo

Congreso; XXI Congreso Latinoamericano de Microbiología (XXI ALAM); 2012

Sociedad Latino Americana de Microbiologia

The RcsCDB regulatory system of Salmonella Typhimurium consists of three proteins: the hybrid sensor RcsC, the response regulator RcsB and the histidine-containing phosphotransfer protein RcsD, as an intermediary in the phosphate group transfer from RcsC to RcsB. We demonstrated that transcription of rcsB is controlled by two promoters: i) PrcsDB that controls expression of the rcsD and rcsB genes as an operon, during the exponential growth phase; and ii) PrcsB that is activated in stationary phase and only able to control the rcsB expression. The RcsCDB system is required to controls the expression of flhDC and cps operons (during exponential phase) and bapA gene (in stationary phase). Although the signal that leads the Rcs system activation remains unknown, it occurs under a wide range of conditions such as the rcsC11 constitutive and tolB gene mutations, and the bacterial growth on solid surface. Due to the RcsCDB system complexity, is possible that more of one ligand modulates the expression of rcsB gene acting from one or both promoters. The goal of this work was determine if the ligands are released into the tolB mutant culture medium to control thercsB gene expression, and establish the RcsB-dependent physiological process that are modulate under this condition. To this end, the supernatant obtained from the wild type strain and tolB mutant cultures, growing up to exponential (4 h) or stationary growth phase (8 h), was used as ?conditioned mediums? (CM). Then, the levels of the transcriptional lacZ fusion to flhDC, cps and bapA genes from strain growing in CM measured as β-galactosidase activity were used as reporter of the different RcsB-inducer ligands presence in the tolB-CM. In these assays, the wild-type CM serves as negative control. Moreover, we investigated if the RcsB induction by the ligands is enough to affect the phenotypes in which the above RcsB-dependent genes are involved. Here, we study the motility inhibition, the mucoid colonies and the biofilm formation. Our results demonstrated that both expression of flhDC, cps and bapA and its dependent phenotypes were modulated in the tolB-CM but not in the wild type-CM, only when rcsB was present. These findings allow us to conclude that the Rcs system activator ligands are release into the CM of tolB mutant and that it are able to enter to wild-type strain and activate the system.