Identification of Genes Preferentially Expressed after Phagocytosis by and Involvement of Methionine Sulfoxide Reductases.

Free-living protozoa affect the survival and virulence evolution of pathogens in the environment. In this study, we explored the fate of when co-cultured with the bacteriovorous ciliate and investigated bacterial gene expression associated with the co-culture. Virulent strains were found to have ability to evade digestion in the vacuoles of this protozoan. In , a total of 116 genes were identified as up-regulated following co-culture with by selective capture of transcribed sequences (SCOTS) and comparative dot-blot analysis. A large proportion of these genes (42/116) play a role in metabolism, and some of the genes have previously been characterized as required for bacterial survival and replication within macrophages. Then, we inactivated the genes encoding methionine sulfoxide reductases, , and , in . Compared to the wild-type, the mutants Δ and Δ displayed significantly reduced resistance to predation by , and 50% lethal dose (LD) determinations in zebrafish demonstrated that both mutants were highly attenuated. This study forms a solid foundation for the study of mechanisms and implications of bacterial defenses.