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Overproduction of DNA Adenine Methyltransferase Alters Motility, Invasion, and the Lipopolysaccharide O-Antigen Composition of Yersinia enterocolitica

Stefan Fälker, Jennifer Schilling, M. Alexander Schmidt, and Gerhard Heusipp^*

Institut für Infektiologie, Zentrum für Molekularbiologie der Entzündung, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

Received 29 March 2007/ Returned for modification 3 May 2007/ Accepted 14 July 2007

DNA adenine methyltransferase (Dam) not only regulates basic cellular functions but also interferes with the proper expression of virulence factors in various pathogens. We showed previously that for the human pathogen Yersinia enterocolitica, overproduction of Dam results in increased invasion of epithelial cells. Since invasion and motility are coordinately regulated in Y. enterocolitica, we analyzed the motility of a Dam-overproducing (Dam^OP) strain and found it to be highly motile. In Dam^OP strains, the operon encoding the master regulator of flagellum biosynthesis, flhDC, is upregulated. We show that the increased invasion is not due to enhanced expression of known and putative Y. enterocolitica invasion and adhesion factors, such as Inv, YadA, Ail, Myf fibrils, Pil, or Flp pili. However, overproduction of Dam no longer results in increased invasion for an inv mutant strain, indicating that Inv is necessary for increased invasion after overproduction of Dam. Since we show that overproduction of Dam results in an increased amount of rough lipopolysaccharide (LPS) molecules lacking O-antigen side chains, this implies that reduced steric hindrance by LPS might contribute to increased invasion by a Y. enterocolitica Dam^OP strain. Our data add an important new aspect to the various virulence-associated phenotypes influenced by DNA methylation in Y. enterocolitica and indicate that Dam targets regulatory processes modulating the composition and function of the bacterial surface.

Published ahead of print on 6 August 2007.

Editor: J. B. Bliska

Present address: Department of Bacteriology, Swedish Institute for Infectious Disease Control, Solna, Sweden.