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Journal of Bacteriology, December 2005, p. 8385-8394, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8385-8394.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Simultaneous Deficiency of both MurA and p60 Proteins Generates a Rough Phenotype in Listeria monocytogenes

Institute of Medical Microbiology, Justus-Liebig-Universität, 35392 Giessen,¹ Department of Microbial Pathogenesis and Vaccine Research, German Centre for Biotechnology (GBF), 38124 Braunschweig, Germany²

Received 24 June 2005/ Accepted 23 September 2005

We examined eight spontaneously occurring rough mutants of Listeria monocytogenes for their ability to express two previously reported autolysins, p60 and MurA. All mutants lack MurA expression and show strongly reduced levels of extracellular p60. One rough strain harbors a variant of the p60 protein with a partially truncated catalytic domain. In seven cases there were shifts in the localization of p60 to the membrane fraction. Mutations within the secA2 gene, encoding an auxiliary protein secretion system paralog, were previously shown to be involved in the smooth-rough phenotypic variation seen with Listeria strains. An isogenic secA2 EGDe deletion strain displays a strong pleiotropic reduction of p60 and MurA, in addition to a large number of secreted and surface proteins. However, we observed no apparent SecA2 dysfunction in several of the investigated strains as determined by direct sequencing of the secA2 gene and complementation of the secA2 mutant with the respective allele cloned from the rough mutant. To determine the gene products required for the smooth-rough transition, we created mutants lacking the individual iap and murA genes as well as a iap murA double mutant. The double mutant displays a rough phenotype and exhibits many of the properties seen with the secA2 mutant. Our results implicate p60 and MurA as important determinants in controlling the cell shape of L. monocytogenes. We also identified homologous MurA and SecA2 proteins in other Listeria species. The muramidase in two species, L. innocua and L. welshimeri, shows activity similar to that of the MurA protein in L. monocytogenes.

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