The LysR-type transcriptional regulator LeuO controls the expression of several genes in Salmonella enterica Serovar Typhi

Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, México; Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, México

^* To whom correspondence should be addressed. Email: ecalva{at}ibt.unam.mx.

	Abstract

LeuO is a LysR-type transcriptional regulator that has been implicated in the bacterial stringent response and in the virulence of Salmonella. A genomic approach in Salmonella enterica Serovar Typhi revealed that LeuO is a positive regulator of OmpS1, OmpS2, AssT, and STY3070. In contrast, LeuO down-regulated the expression of OmpX, Tpx and STY1978. Transcriptional fusions supported the positive and negative LeuO regulation. Expression of ompS1, assT and STY3070 was induced in an hns mutant, consistent with the notion that H-NS represses these genes; transcriptional activity was lowered for tpx and STY1978 in an hns background, suggesting a positive effect by this global regulatory protein. In contrast, ompS2 and ompX expression appeared to be H-NS-independent. LeuO specifically bound to the 5' intergenic regions of ompS2, assT, STY3070, ompX, and tpx while it was not observed to bind to the promoter region of STY1978, suggesting that LeuO is regulating in a direct and indirect manner, respectively. In this work, a novel set of genes belonging to the LeuO regulon are reported, interestingly, these genes are involved in a variety of biological processes suggesting that LeuO is a global regulator in Salmonella.