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Journal of Bacteriology, March 2009, p. 1868-1877, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01481-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of the Escherichia coli O157:H7 Sakai GadE Regulon{triangledown} ,{dagger}

Sivapriya Kailasan Vanaja,* Teresa M. Bergholz,{ddagger} and Thomas S. Whittam

Microbial Evolution Laboratory, National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824

Received 20 October 2008/ Accepted 22 December 2008

Integrating laterally acquired virulence genes into the backbone regulatory network is important for the pathogenesis of Escherichia coli O157:H7, which has captured many virulence genes through horizontal transfer during evolution. GadE is an essential transcriptional activator of the glutamate decarboxylase (GAD) system, the most efficient acid resistance (AR) mechanism in E. coli. The full contribution of GadE to the AR and virulence of E. coli O157:H7 remains largely unknown. We inactivated gadE in E. coli O157:H7 Sakai and compared global transcription profiles of the mutant with that of the wild type in the exponential and stationary phases of growth. Inactivation of gadE significantly altered the expression of 60 genes independently of the growth phase and of 122 genes in a growth phase-dependent manner. Inactivation of gadE markedly downregulated the expression of gadA, gadB, and gadC and of many acid fitness island genes. Nineteen genes encoded on the locus of enterocyte effacement (LEE), including ler, showed a significant increase in expression upon gadE inactivation. Inactivation of ler in the {Delta}gadE strain reversed the effect of gadE deletion on LEE expression, indicating that Ler is necessary for LEE repression by GadE. GadE is also involved in downregulation of LEE expression under conditions of moderately acidic pH. Characterization of AR of the {Delta}gadE strain revealed that GadE is indispensable for a functional GAD system and for survival of E. coli O157:H7 in a simulated gastric environment. Altogether, these data indicate that GadE is critical for the AR of E. coli O157:H7 and that it plays an important role in virulence by downregulating expression of LEE.

* Corresponding author. Mailing address: NFSTC, 195 Food Safety and Toxicology Building, Michigan State University, East Lansing, MI 48824. Phone: (517) 884-2034. Fax: (517) 432-2310. E-mail: kailasan{at}msu.edu

{triangledown} Published ahead of print on 29 December 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: 405 Stocking Hall, Department of Food Science, Cornell University, Ithaca, NY 14853.

Journal of Bacteriology, March 2009, p. 1868-1877, Vol. 191, No. 6
0021-9193/09/$08.00+0     doi:10.1128/JB.01481-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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