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J. Bacteriol. doi:10.1128/JB.01073-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The flagellar muramidase from the photosynthetic bacterium Rhodobacter sphaeroides

Instituto de Fisiología Celular, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México

^* To whom correspondence should be addressed. Email: gdreyfus{at}ifc.unam.mx.

	Abstract

We have carried out the characterization of an open reading frame (orf) RSP0072, which is located within the flgG operon in Rhodobacter sphaeroides. The amino acid sequence analysis of this gene product showed the presence of a soluble lytic transglycosylase domain (slt). The deletion of the N-terminal region (112 aa) of the product of RSP0072 renders a non-motile phenotype as determined by swarm assays in soft agar. Electron micrographs revealed the lack of flagellum in the mutant cells. The purified wild-type protein showed lytic activity on extracts of M. lysodeikticus. In contrast, no lytic activity was observed when the residues E57 or E83 were replaced by alanine. Affinity blotting suggests that the protein encoded by RSP0072 interacts with the flagellar rod-scaffolding protein FlgJ, which lacks the muramidase domain present in FlgJ of many bacteria. We propose that the product of RSP0072 is a flagellar muramidase that is exported to the periplasm via the Sec pathway where it interacts with FlgJ to open a gap in the peptidoglycan layer for the subsequent penetration of the nascent flagellar structure.