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J. Bacteriol. doi:10.1128/JB.01348-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The enterobacterial common antigen (ECA) integrity is a checkpoint for flagellar biogenesis in Serratia marcescens

Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Técnicas, Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina; Department of Biological Sciences, University of Alberta, T6G 2E9 Edmonton, Alberta, Canada

^* To whom correspondence should be addressed. Email: garciavescovi{at}ibr.gov.ar.

	Abstract

Serratia marcescens are ubiquitous bacteria isolated from environmental niches such as soil, water, and air, that also constitute emergent nosocomial opportunistic pathogens. Among the numerous extracellular factors that S. marcescens is able to produce, the PhlA phospholipase is the only described exoprotein secreted by the flagellar apparatus, while simultaneously being a member of the flagellar regulon. To gain an insight into the regulatory mechanism that couples PhlA and flagellar expression, we conducted a generalized insertional mutagenesis and screened for PhlA deficient strains. We found that three independent mutations in the wec cluster which impaired the enterobacterial common antigen (ECA) assembly provoked the inhibition of PhlA expression. Swimming and swarming assays showed that, in these strains, motility was severely affected. Microscopic examination and flagellin immunodetection demonstrated that a strong defect in flagella expression was responsible for the reduced motility in the wec mutant strains. Furthermore, we determined that in the ECA-defective strains the transcriptional cascade that controls flagellar assembly was turned off due to the down-regulation of flhDC expression. These findings open a new perspective in the physiological role of the ECA, providing evidence that in S. marcescens its biosynthesis conditions the expression of the flagellar regulon.

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