LcrV synthesis is altered by DNA adenine methylase overproduction in Yersinia pseudotuberculosis and is required to confer immunity in vaccinated hosts

Yersinia pseudotuberculosis mutants that overproduce the DNA adenine methylase (Dam(OP) Yersinia) are attenuated, confer robust protective immune responses, and synthesize or secrete several Yersinia outer proteins (Yops) under conditions that are nonpermissive for synthesis and secretion in wild-type strains. To understand the molecular basis of immunity elicited by Dam(OP) Yersinia, we investigated the effects of Dam overproduction on the synthesis and localization of a principal Yersinia immunogen, LcrV, a low-calcium-responsive virulence factor involved in Yop synthesis, localization, and suppression of host inflammatory activities. Dam overproduction relaxed the stringent temperature and calcium regulation of LcrV synthesis. Moreover, the LcrV-dependent synthesis and localization of the actin cytotoxin, YopE, were shown to be relaxed in Dam(OP) cells, suggesting that the synthesis and localization of Yops can occur via both LcrV-dependent and -independent mechanisms. Last, the immunity conferred by Dam(OP) Yersinia was strictly dependent on the presence of LcrV, which may result from its role (i) as an immunogen, (ii) as an immunomodullator of host anti-inflammatory activities, or (iii) in the altered synthesis and localization of Yops that could contribute to immunogen repertoire expansion.