Insights into and gene regulation on the virulence of M5-90.

Iron is a fundamental element required by most organisms, including . Several researchers have suggested that the iron response regulator () and rhizobial iron regulator () genes regulate iron acquisition by , influencing heme synthesis by and virulence of this pathogen. However, little is known about another species, . In this research, we successfully constructed two mutants: M5-90Δ and M5-90Δ. The adhesion, invasion, and intracellular survivability of these two mutants were evaluated in RAW264.7 cells infected with 1 × 10 CFU of M5-90Δ, M5-90Δ, or M5-90. We also tested the sensitivity of cells to hydrogen peroxide and their ability to grow. In addition, the virulence of these two mutants was evaluated in BALB/c mice. The results showed that the ability of these two mutants to invade and adhere inside the murine macrophages RAW264.7 was attenuated but their ability to replicate intracellularly was strengthened, enhancing the resistance to hydrogen peroxide. The M5-90Δ mutant showed stronger growth ability than the parental strain under iron-limiting conditions. No differences were observed in the number of bacteria in spleen between M5-90 and M5-90Δ at 7 or 15 days postinfection. However, the number of M5-90Δ in spleen reduced significantly at 15 days postinfection. The splenic index of the M5-90Δ group is evidently lower than that of M5-90. This is the first report that and genes of are associated not only with virulence but also with growth ability. Together, our data suggest that M5-90Δ is a promising vaccine candidate.