Differential regulation of the two oligogalacturonate outer membrane channels KdgN and KdgM of Dickeya dadantii (Erwinia chrysanthemi)

Université de Lyon, F-69003, France; Université Lyon 1, F-69622; INSA-Lyon, Villeurbanne, F-69621; CNRS, UMR5240, Unité Microbiologie Adaptation et Pathogénie, F-69622, France; and Groupe canaux ioniques, CNRS UMR8619, Université Paris-Sud, F-91405 Orsay

^* To whom correspondence should be addressed. Email: guy.condemine{at}insa-lyon.fr.

	Abstract

Entry of oligogalacturonates into Dickeya dadantii occurs through the specific channel KdgM. The genome of the bacteria encodes a second member of this family of outer membrane proteins, KdgN. We showed that this protein is also involved in the uptake of oligogalacturonates. When KdgN was reconstituted in proteoliposomes, it formed channels with a conductance of about 450 pS at positive potential. These channels had a weak anionic selectivity. Regulation of kdgN is complex and five genes controlling its expression have been identified: kdgR, pecS, ompR, hns and crp. Moreover, kdgN is regulated by growth phase but only when bacteria were grown in rich medium. Most of these regulators of kdgN also control kdgM expression but for some of them, the regulation is opposite: while PecS and OmpR are repressors of kdgM they are activators of kdgN. This looks like the regulation of the Escherichia coli general porins OmpF and OmpC, but such opposite regulation of two specific outer membrane channels has never been described before. KdgN could allow the bacteria to collect oligogalacturonates in saprophytic conditions, when virulence genes, including kdgM, are not expressed.