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Infection and Immunity, March 2005, p. 1684-1694, Vol. 73, No. 3
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.3.1684-1694.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

HosA, a Member of the SlyA Family, Regulates Motility in Enteropathogenic Escherichia coli

Maria-José Ferrándiz,1,{dagger} Keith Bishop,1 Paul Williams,1 and Helen Withers1*

Institute of Infection, Immunity and Inflammation, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, United Kingdom1

Received 29 June 2004/ Returned for modification 23 July 2004/ Accepted 8 November 2004

In enteropathogenic and enterohemorraghic Escherichia coli (EPEC and EHEC), two members of the SlyA family of transcriptional regulators have been identified as SlyA. Western blot analysis of the wild type and the corresponding hosA and slyA deletion mutants indicated that SlyA and HosA are distinct proteins whose expression is not interdependent. Of 27 different E. coli strains (EPEC, EHEC, enteroinvasive, enteroaggregative, uropathogenic, and commensal) examined, 14 were positive for both genes and proteins. To investigate hosA expression, a hosA::luxCDABE reporter gene fusion was constructed. hosA expression was significantly reduced in the hosA but not the slyA mutant and was influenced by temperature, salt, and pH. In contrast to SlyA, HosA did not activate the cryptic E. coli K-12 hemolysin ClyA. Mutation of hosA did not influence type III secretion, the regulation of the LEE1 and LEE4 operons, or the ability of E2348/69 to form attaching-and-effacing lesions on intestinal epithelial cells. HosA is, however, involved in the temperature-dependent positive control of motility on swim plates and regulates fliC expression and FliC protein levels. In electrophoretic mobility shift assays, purified HosA protein bound specifically to the fliC promoter, indicating that HosA directly modulates flagellin expression. While direct examination of flagellar structure and the motile behavior of individual hosA cells grown in broth culture at 30°C did not reveal any obvious differences, hosA mutants, unlike the wild type, clumped together, forming nonmotile aggregates which could account for the markedly reduced motility of the hosA mutant on swim plates at 30°C. We conclude that SlyA and HosA are independent transcriptional regulators that respond to different physicochemical cues to facilitate the environmental adaptation of E. coli.

* Corresponding author. Present address: Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. Phone: 64 9 3737599. Fax: 64 9 3737492. E-mail: h.withers{at}auckland.ac.nz.

Editor: J. B. Bliska

{dagger} Present address: Centro Nacional de Microbiologia, Instituto de Salud Carlos III, Madrid, Spain.

Infection and Immunity, March 2005, p. 1684-1694, Vol. 73, No. 3
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.3.1684-1694.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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