DNA Adenine Methyltransferase (Dam) Overexpression Impairs Motility and Virulence.

Dam, the most described bacterial DNA-methyltransferase, is widespread in gamma-proteobacteria. Dam DNA methylation can play a role in various genes expression and is involved in pathogenicity of several bacterial species. The purpose of this study was to determine the role played by the ortholog identified in the entomopathogenic bacterium . Complementation assays of an mutant showed the restoration of the DNA methylation state of the parental strain. Overexpression of in did not impair growth ability . In contrast, compared to a control strain harboring an empty plasmid, a significant decrease in motility was observed in the -overexpressing strain. A transcriptome analysis revealed the differential expression of 208 genes between the two strains. In particular, the downregulation of flagellar genes was observed in the -overexpressing strain. In the closely related bacterium overexpression also impaired motility. In addition, the -overexpressing strain showed a delayed virulence compared to that of the control strain after injection in larvae of the lepidopteran . These results reveal that Dam plays a major role during insect infection.