PRFA-LIKE TRANSCRIPTION FACTOR, LMO0753, CONTRIBUTES TO VIRULENCE, L-RHAMNOSE UTILIZATION, AND PERSISTENCE OF LISTERIA MONOCYTOGENES HUMAN FOODBORNE OUTBREAK LINEAGES

Listeria monocytogenes is a foodborne bacterial pathogen and the causative agent of a human and animal disease, listeriosis. Among the three major genetic lineages of L. monocytogenes (i.e. LI, LII, and LIII), LI and LII are predominantly associated with foodborne listeriosis outbreaks, whereas LIII is rarely implicated in human infections. In a previous study, we identified a Crp/Fnr family transcription factor lmo0753 that was highly specific to outbreak-associated LI and LII but absent from LIII. Lmo0753 shares two conserved functional domains including a DNA-binding domain with the well-characterized master virulence regulator PrfA in L. monocytogenes. In this study, lmo0753 deletion and complementation mutants were constructed in two fully sequenced L. monocytogenes LII strains 10403S and EGDe, and compared virulence-associated mechanisms of flagellar motility, phospholipase C production, hemolysis, and intracellular growth of the mutants and their respective wild types. Persistence-associated mechanisms of growth, biofilm production, attachment and soil survival were also assayed. Results suggested that lmo0753 plays a role in some virulence- and persistence-associated mechanisms in both EGDe and 10403S. More importantly, it was found that deletion of lmo0753 led to the loss of L-rhamnose utilization in EGDe but not in 10403S. Transcriptomic comparison of the EGDe lmo0753 deletion mutant and the wild type incubated in Phenol-red medium containing L-rhamnose as the sole carbon source revealed 126 (4.5%) and 546 (19.5%) out of 2,798 genes in the EGDe genome that were up- and down-regulated for more than 2-fold, respectively. Genes involved in biotin biosynthesis, general stress response and rhamnose metabolism were shown to be differentially regulated by Lmo0753. Findings from this study may partially explain why xvi LIII of L. monocytogenes is underrepresented in the environment and rarely associated with human listeriosis outbreaks due to the inability of rhamnose utilization.PH.D in Biology, December 201