Project Summary/Abstract Listeria monocytogenes is facultative intracellular food-borne pathogen that provides an extremely amenable model for basic studies on host-pathogen interactions. During past funding periods, genetic screens led to the discovery that L. monocytogenes upregulates the expression and synthesis of glutathione synthase (GshF) during infection and that glutathione is an allosteric activator of the major virulence transcription factor, PrfA. Mutants lacking GshF fail to fully activate PrfA and consequently form small plaques in tissue culture cells and are approximately 200-fold less virulent in mice. However, virulence of gshF mutants was fully rescued by mutations that locked PrfA in its active configuration, referred to as PrfA* mutants. During the current funding period, we designed a genetic screen with the goal of identifying additional transposon mutants that formed small plaques in tissue culture cells, but were restored to a wild- type phenotype when the mutation was transduced into a PrfA* background. In addition to finding the expected gshF mutants, we found mutants in gloA, which encodes glyoxalase A, the primary component necessary for the glutathione-dependent detoxification of the reactive electrophilic species (RES), methylglyoxal (MGO), which is a toxic side-product of glycolysis in both bacteria and host cells. Mutants lacking gloA were approximately 1000-fold less virulent in mice and like gshF mutants, were restored to full virulence in a PrfA* background, suggesting that MGO is an in vivo cue leading to GshF synthesis and activation of PrfA. MGO reacts with both amino acids and guanine causing DNA damage and mutations. In preliminary data, we confirmed that gloA mutants had a 10-fold increase in their mutation rate when exposed to MGO in vitro, but strikingly, the mutation rate of gloA mutants was approximately 100-1000-fold higher in the spleens and livers of infected mice, suggesting that the in vivo environment encountered by L. monocytogenes is enriched in MGO and consequently highly mutagenic. Double gloA/prfA* mutants were not only fully virulent, they did not suffer increased mutation rates in vivo, suggesting that in the absence of GloA, activated PrfA protects against DNA damage by a yet-to-be discovered mechanism. Based on the literature, we hypothesized that DNA damage caused by MGO was repaired by UvrAB-dependent nucleotide excision repair pathway. Astonishingly, a uvrAB mutation rescued the virulence defect of gloA mutants, but unlike PrfA* mutants, gloA/uvrAB mutants still had an extremely high mutation rate. These data suggest that gloA mutants suffer severe DNA damage in vivo and are killed by the resultant DNA repair process. In this renewal, we propose to characterize the in vivo environment that causes such a high rate of mutations in gloA mutants, determine how PrfA mediates GloA-independent protections from MGO, and lastly explore the hypothesis that gloA mutants are killed by their own ...