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ppGpp-dependent Stationary Phase Induction of Genes on Salmonella Pathogenicity Island 1

2004; Elsevier BV; Volume: 279; Issue: 33 Linguagem: Inglês

10.1074/jbc.m313491200

1083-351X

Mi‐Ryoung Song, Hyun-Ju Kim, Eun Young Kim, Minsang Shin, Hyun Chul Lee, Yeongjin Hong, Joon Haeng Rhee, Hyunjin Yoon, Sangryeol Ryu, Sangyong Lim, Hyon E. Choy,

Bacterial Genetics and Biotechnology

We have examined expression of the genes on Salmonella pathogenicity island 1 (SPI1) during growth under the physiologically well defined standard growth condition of Luria-Bertani medium with aeration. We found that the central regulator hilA and the genes under its control are expressed at the onset of stationary phase. Interestingly, the two-component regulatory genes hilC/hilD , sirA/barA , and ompR , which are known to modulate expression from the hilA promoter ( hilA p) under so-called "inducing conditions" (Luria-Bertani medium containing 0.3 m NaCl without aeration), acted under standard conditions at the stationary phase induction level. The induction of hilA p depended not on RpoS, the stationary phase sigma factor, but on the stringent signal molecule ppGpp. In the ppGpp null mutant background, hilA p showed absolutely no activity. The stationary phase induction of hilA p required spoT but not relA . Consistent with this requirement, hilA p was also induced by carbon source deprivation, which is known to transiently elevate ppGpp mediated by spoT function. The observation that amino acid starvation elicited by the addition of serine hydroxamate did not induce hilA p in a RelA + SpoT + strain suggested that, in addition to ppGpp, some other alteration accompanying entry into the stationary phase might be necessary for induction. It is speculated that during the course of infection Salmonella encounters various stressful environments that are sensed and translated to the intracellular signal, ppGpp, which allows expression of Salmonella virulence genes, including SPI1 genes.