Submitted to: Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/15/2005
Publication Date: 5/31/2005
Citation: Uhlich, G.A., Wonderling, L., Luchansky, J.B. 2005. Analyses of the putative crp/fnr family of transcriptional regulators of a serotype 4b strain of listeria monocytogenes. Food Microbiology. Available: http://www.sciencedirect.com/science. Interpretive Summary: The purpose of this study was to analyze the function of a group of potential regulatory genes, identified in a food outbreak strain of Listeria monocytogenes. These genes, which are present in an unusually high number in L. monocytogenes, are similar to an important family of the regulatory genes (Crp/Fnr family) found in many other bacteria that control other genes involved primarily in respiration, metabolism, and/or resistance to oxidative stress. Using molecular techniques we individually inactivated each of these regulatory genes and compared them in a series of assays designed to reveal the functions controlled by each regulatory gene. We determined that none of the genes was involved in the regulation of growth under reduced oxygen conditions or in the control of the metabolism of sugars used as their primary sources of energy. However, certain genes were shown to be required for maximal resistance of the bacteria to oxidative stresses. Therefore, this family of genes regulates certain functions, similar to the previously described gene families of other bacteria, which may enhance the survival of L. monocytogenes in foods or in the processing environment.
Technical Abstract: 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 readily utilized carbon sources of L. monocytogenes. Although strain KO2 had a reduced growth rate compared to strain F2365 and the other mutant strains at 30oC but not at 37oC, there were no differences in growth rates among strain F2365 and the mutant strains when incubated at either 30o or 37o 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.