Salmonella typhimurium Encodes an SdiA Homolog, a Putative Quorum Sensor of the LuxR Family, That Regulates Genes on the Virulence Plasmid

Abstract

Quorum sensing is a phenomenon in which bacteria sense and respond to their own population density by releasing and sensing pheromones. In gram-negative bacteria, quorum sensing is often performed by the LuxR family of transcriptional regulators, which affect phenotypes as diverse as conjugation, bioluminescence, and virulence gene expression. The gene encoding one LuxR family member, named sdiA(suppressor of cell division inhibition), is present in theEscherichia coli genome. In this report, we have cloned theSalmonella typhimurium homolog of SdiA and performed a systematic screen for sdiA-regulated genes. A 4.4-kb fragment encoding the S. typhimurium sdiA gene was sequenced and found to encode the 3′ end of YecC (homologous to amino acid transporters of the ABC family), all of SdiA and SirA (Salmonella invasion regulator), and the 5′ end of UvrC. This gene organization is conserved between E. coli andS. typhimurium. We determined that the S. typhimurium sdiA gene was able to weakly complement the E. coli sdiA gene for activation of ftsQAZ at promoter 2 and for suppression of filamentation caused by an ftsZ(Ts) allele. To better understand the function of sdiA inS. typhimurium, we screened 10,000 random lacZYtranscriptional fusions (MudJ transposon mutations) for regulation bysdiA. Ten positively regulated fusions were isolated. Seven of the fusions were within an apparent operon containing ORF8, ORF9,rck (resistance to complement killing), and ORF11 of theS. typhimurium virulence plasmid. The three ORFs have now been named srgA, srgB, and srgC(for sdiA-regulated gene), respectively. The DNA sequence adjacent to the remaining three fusions shared no similarity with previously described genes.

Quorum sensing: the many languages of bacteria

“…The precise role of SdiA in QS was elusive for several years until Michael et al (2001) reported that SdiA is not sensing an autoinducer produced by Salmonella itself, but rather AHLs produced by other bacterial species. SdiA regulates a few genes in Salmonella including one gene potentially involved in resistance to human complement, rck (Ahmer et al, 1998). However, mutation of the sdiA gene had no effect on virulence of Salmonella in mouse, chicken or bovine models of disease (Ahmer, 2004).…”

High-level resistance to mecillinam produced by inactivation of soluble lytic transglycosylase in Salmonella enterica serovar Typhimurium

“…DNA flanking the left end of insertion slt-1::MudJ was obtained as described by Ahmer et al (1998). To enrich the template DNA in the chromosomal region of S. thyphimurium corresponding to centisome 0 were the insertion appeared to map, an slt-1::MudJ derivative of strain TT15224 (Benson & Goldman, 1992) was obtained by transduction.…”

Salmonellastress management and its relevance to behaviour during intestinal colonisation and infection

“…sdiA in Salmonella was first described by Ahmer et al [167] when this group suggested a link between sdiA and positive regulation of ten genes on the virulence plasmid including the previously characterised rck gene responsible for increased resistance to complement killing and adhesion to epithelial cells [168]. Although sdiA in S. typhimurium seems to be suppressed by conditioned medium to the extent observed in E. coli [169], no AI-1 like metabolite was ever detected also in S. typhimurium conditioned media.…”