CONICET | Buscador de Institutos y Recursos Humanos

Bacterial cells have the ability to survive and respond to adverse changes in theenvironment in which they are living, by regulating gene transcription throughout twocomponentregulatory systems. It has been reported that in SalmonellaTyphimurium, STM1485 gene expression is induced under low pH conditions (pH 4.5),mainly during the replication within host. However, this gene product of is not directlyinvolved in sensing or resistance to acidic conditions, and the mechanisms that controlits gene expression remains unknown. Since the RcsCDB system is induced underacidic conditions, we investigated whether this system is capable to modulate theSTM1485 expression. We here demonstrated that the RcsCDB system acid-activationrepresses the STM1485 transcription by directly binding to the promoter.Physiologically, this repression is required for bacterial survival when it is exposed topancreatic fluids. However, when the pathogen reached the epithelial cells barrier, thesurviving bacteria can invade and remain confined in vacuolar structures. In this newenvironment, the acidic and magnesium starvation conditions induce the RstAregulator, in PhoPQ-dependent manner, which binds the promoter of STM1485 toinduce once again its expression. These increased levels would allow the invasion andreplication of Salmonella in the vacuoles to continue with the following infectionsteps. We here suggest that this gene product plays an important role inSalmonella adaptation to pH changes during transition on gastrointestinal tract.In addition, we performed the promoter sequence analysis of E. coli asr andSalmonella STM1485 homologous genes, and we observed the absence of a34 bp region in Salmonella, where EvgA and PhoB transcriptional factors arebinding to also control asr expression. These results allow us to suggest thateven when both gene products are involved in the same acid response, each bacterialspecies responds by different signal transduction pathways.