DNA adenine methylase is involved in the pathogenesis of Edwardsiella tarda

Edwardsiella tarda is a serious aquaculture pathogen that can infect many cultured fish species. The aim of this study was to investigate the potential importance of DNA adenine methylase (Dam) in E. tarda pathogenesis. The E. tarda dam gene (damEt) was cloned from a pathogenic strain, TXD1, isolated from diseased fish. DamEt shares high (70.2%) sequence identity with the Dam proteins of Yersinia enterocolitica and several other bacterial species. Recombinant DamEt is able to complement a dam-deficient Escherichia coli strain and methylate the genomic DNA. Attenuation of damEt expression by antisense RNA interference had no apparent effect on the growth of TXD1, but caused significant attenuation of overall bacterial virulence and altered several stress responses including spontaneous mutation, recovering from UV radiation and H2O2 exposure, binding to host mucus, and dissemination in host blood and liver. In addition, attenuation of damEt expression increased luxS expression and AI-2 activities in E. tarda. These results indicate that DamEt is a virulence determinant and plays a role in the pathogenesis of TXD1, and that temporal expression of damEt is essential for optimal bacterial infection.