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J. Bacteriol. doi:10.1128/JB.01483-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

PhyR is involved in the general stress response of Methylobacterium extorquens AM1

Institute of Microbiology, ETH Zurich, 8093 Zurich, Switzerland

^* To whom correspondence should be addressed. Email: vorholt{at}micro.biol.ethz.ch.

	Abstract

PhyR represents a novel alphaproteobacterial family of response regulators having a structure consisting of two domains; a predicted amino terminal extracytoplasmic function (ECF) sigma factor-like domain and a carboxy terminal receiver domain. PhyR was first described in Methylobacterium extorquens AM1 where it has been shown to be essential for plant colonization, probably due to its suggested involvement in the regulation of a number of stress proteins. Here we investigate the PhyR regulon using microarray technology. We found the PhyR regulon to be rather large, with most of the 246 targets under positive control. Mapping of transcriptional start sites revealed candidates promoters for PhyR mediated regulation. One of these, an ECF type promoter, was identified upstream one third of target genes by in silico analysis. Among PhyR targets are genes predicted to be involved in multiple stress responses including katE, osmC, htrA, dnaK, gloA, dps, and uvrA. The induction of these genes is consistent with our phenotypic analyses which revealed that PhyR is involved in resistance to heat shock and desiccation as well as oxidative, UV, ethanol and osmotic stress in M. extorquens AM1. The finding that PhyR is involved in general stress response was further substantiated by the finding that carbon starvation induces protection against heat shock and that this protection is at least in part dependent on PhyR.