ppGpp-dependent stationary phase induction of genes on Salmonella pathogenicity island 1.
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 (hilAp) 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 hilAp depended not on RpoS, the stationary phase sigma factor, but on the stringent signal molecule ppGpp. In the ppGpp null mutant background, hilAp showed absolutely no activity. The stationary phase induction of hilAp required spoT but not relA. Consistent with this requirement, hilAp 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 hilAp 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.
Song
Miryoung
M
Genome Research Center for Enteropathogenic Bacteria and Research Institute of Vibrio Infection, Chonnam National University Medical College, Kwangju 501-746, South Korea.
Kim
Hyun-Ju
HJ
Kim
Eun Young
EY
Shin
Minsang
M
Lee
Hyun Chul
HC
Hong
Yeongjin
Y
Rhee
Joon Haeng
JH
Yoon
Hyunjin
H
Ryu
Sangryeol
S
Lim
Sangyong
S
Choy
Hyon E
HE
D001426:Bacterial Proteins; D002455:Cell Division; D002460:Cell Line; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands; D006159:Guanosine Tetraphosphate / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012475:Salmonella / Q000378:metabolism*; D012480:Salmonella Infections / Q000378:metabolism*; D012965:Sodium Chloride / Q000737:chemistry; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
D001426:Bacterial Proteins; D003470:Culture Media; C102236:HilA protein, Salmonella; D015534:Trans-Activators; D006159:Guanosine Tetraphosphate; D012965:Sodium Chloride; D001616:beta-Galactosidase