Open AccessTranscription of the ehx Enterohemolysin Gene Is Positively Regulated by GrlA, a Global Regulator Encoded within the Locus of Enterocyte Effacement in Enterohemorrhagic Escherichia coli
Author(s) -
Takehito Saitoh,
Sunao Iyoda,
Shouji Yamamoto,
Yan Lu,
Ken Shimuta,
Makoto Ohnishi,
Jun Terajima,
Haruo Watanabe
Publication year - 2008
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.00231-08
Subject(s) - biology , gene , pathogenicity island , mutant , virulence , transcription (linguistics) , plasmid , regulator gene , escherichia coli , locus (genetics) , regulation of gene expression , psychological repression , gene expression , transcription factor , genetics , linguistics , philosophy
The pathogenicity island termed locus of enterocyte effacement (LEE) encodes a type 3 protein secretion system, whose function is required for full virulence of enterohemorrhagicEscherichia coli (EHEC). GrlR and GrlA are LEE-encoded negative and positive regulators, respectively, for controlling transcription of theler gene, which encodes a central activator of LEE gene expression. We previously reported that the GrlR-GrlA regulatory system controls not only the LEE genes but also flagellar gene expression in EHEC (S. Iyoda et al., J. Bacteriol.188: 5682-5692, 2006). In order to further explore virulence-related genes under the control of the GrlR-GrlA regulatory system, we characterized agrlR -deleted EHEC O157 strain, which was found to have high and low levels of expression of LEE and flagellar genes, respectively. We report here that thegrlR deletion significantly induced enterohemolysin (Ehx) activity of EHEC O157 on plates containing defibrinated sheep erythrocytes. Ehx levels were not induced in thegrlR grlA double mutant strain but increased markedly by overexpression of GrlA even in theler mutant, indicating that GrlA is responsible for this regulation. Ehx of the EHEC O157 Sakai strain is encoded by theehxCABD genes, which are carried on the large plasmid pO157. The expression ofehxC fused with FLAG tag or a promoterlesslacZ gene on pO157 was significantly induced under conditions in which GrlA was overproduced. These results together suggest that GrlA acts as a positive regulator for theehx transcription in EHEC.