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Journal of Bacteriology, August 2008, p. 5256-5264, Vol. 190, No. 15
0021-9193/08/$08.00+0     doi:10.1128/JB.01536-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Modulation of Hexa-Acyl Pyrophosphate Lipid A Population under Escherichia coli Phosphate (Pho) Regulon Activation{triangledown}

Martin G. Lamarche,1 Sang-Hyun Kim,2,3 Sébastien Crépin,1 Michael Mourez,1 Nicolas Bertrand,1 Russell E. Bishop,2 J. Daniel Dubreuil,1 and Josée Harel1*

Groupe de Recherche sur les Maladies Infectieuses du Porc, Université de Montréal, Faculté de Médecine Vétérinaire, C.P. 5000, Saint-Hyacinthe, Québec, Canada J2S 7C6,1 Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada L8N 3Z5,2 The National Primate Research Center, KRIBB, OChang, Chungbuk 363-883, Republic of Korea3

Received 24 September 2007/ Accepted 22 May 2008

Environmental phosphate is an important signal for microorganism gene regulation, and it has recently been shown to trigger some key bacterial virulence mechanisms. In many bacteria, the Pho regulon is the major circuit involved in adaptation to phosphate limitation. The Pho regulon is controlled jointly by the two-component regulatory system PhoR/PhoB and by the phosphate-specific transport (Pst) system, which both belong to the Pho regulon. We showed that a pst mutation results in virulence attenuation in extraintestinal pathogenic Escherichia coli (ExPEC) strains. Our results indicate that the bacterial cell surface of the pst mutants is altered. In this study, we show that pst mutants of ExPEC strains display an increased sensitivity to different cationic antimicrobial peptides and vancomycin. Remarkably, the hexa-acylated 1-pyrophosphate form of lipid A is significantly less abundant in pst mutants. Among differentially expressed genes in the pst mutant, lpxT coding for an enzyme that transfers a phosphoryl group to lipid A, forming the 1-diphosphate species, was found to be downregulated. Our results strongly suggest that the Pho regulon is involved in lipid A modifications, which could contribute to bacterial surface perturbations. Since the Pho regulon and the Pst system are conserved in many bacteria, such a lipid A modification mechanism could be widely distributed among gram-negative bacterial species.

* Corresponding author. Mailing address: Groupe de Recherche sur les Maladies Infectieuses du Porc, Université de Montréal, Faculté de Médecine Vétérinaire, C.P. 5000, Saint-Hyacinthe, Québec, Canada J2S 7C6. Phone: (450) 773 8521, ext. 8233. Fax: (450) 778 8108. E-mail: josee.harel{at}umontreal.ca

{triangledown} Published ahead of print on 30 May 2008.

Journal of Bacteriology, August 2008, p. 5256-5264, Vol. 190, No. 15
0021-9193/08/$08.00+0     doi:10.1128/JB.01536-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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