Analyses of the putative Crp/Fnr family of transcriptional regulators of a serotype 4b strain of Listeria monocytogenes

A whole-genome sequence analysis of Listeria monocytogenes strain F2365 revealed 15 potential members of the Crp/Fnr family of transcriptional regulatory proteins. Each gene and the flanking regions were cloned, subjected to in vitro transpositional mutagenesis, and recombined into strain F2365. Mutant strains, produced for 14 of the family members, were compared to strain F2365 for differences in carbon utilization, resistance to oxidative stress, and growth under reduced oxygen conditions that would signal an Fnr- or Crp-like function for these proteins. There were no differences among strain F2365 and the 14 mutant strains in the utilization of the carbon sources readily utilized by L. monocytogenes. Although strain KO2 had a reduced growth rate compared to strain F2365 and the other mutant strains at 30° but not at 37 °C, there were no differences in growth rates among strain F2365 and the mutant strains when incubated at either 30 or 37 °C under reduced oxygen conditions. However, when compared for differences in response to oxidative stress, mutants KO2 and KO5 showed reduced oxidative stress tolerance compared to the wild-type strain F2365. These results suggest that certain members of the putative Crp/Fnr family in L. monocytogenes may function in response to oxidative stress similar to the Fnr-like protein (Flp) of other Gram-positive bacteria.