prfA -Like Transcription Factor Gene lmo0753 Contributes to l -Rhamnose Utilization in Listeria monocytogenes Strains Associated with Human Food-Borne Infections

Abstract

e Listeria monocytogenes is a food-borne bacterial pathogen and the causative agent of human and animal listeriosis. Among the three major genetic lineages of L. monocytogenes (i.e., LI, LII, and LIII), LI and LII are predominantly associated with food-borne listeriosis outbreaks, whereas LIII is rarely implicated in human infections. In a previous study, we identified a Crp/Fnr family transcription factor gene, 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, we constructed lmo0753 deletion and complementation mutants in two fully sequenced L. monocytogenes LII strains, 10403S and EGDe, and compared the flagellar motility, phospholipase C production, hemolysis, and intracellular growth of the mutants and their respective wild types. Our results suggested that lmo0753 plays a role in hemolytic activity in both EGDe and 10403S. More interestingly, we found that deletion of lmo0753 led to the loss of L-rhamnose utilization in EGDe, but not in 10403S. RNA-seq analysis of EGDe ⌬0753 incubated in phenol red medium containing L-rhamnose as the sole carbon source revealed that 126 (4.5%) and 546 (19.5%) out of 2,798 genes in the EGDe genome were up-and downregulated more than 2-fold, respectively, compared to the wild-type strain. Genes related to biotin biosynthesis, general stress response, and rhamnose metabolism were shown to be differentially regulated. Findings from this study collectively suggested varied functional roles of lmo0753 in different LII L. monocytogenes strain backgrounds associated with human listeriosis outbreaks.

Impact of vitamin B12 on rhamnose metabolism, stress defense and in-vitro virulence ofListeria monocytogenes

“…Notably, despite expression of Pdu proteins, no production of pdu BMC signature metabolites propionate and 1-propanol was detected as shown above (figure 2), in line with our previously reported data [13], that showed only presence of BMCs and activation of pdu BMC in anaerobically rhamnose grown cells with added B12. Our data extend previous RNAseq studies that showed slight increase in pdu expression in the presence of propanediol, and highest expression when B12 was also present [28, 29]. The lack of pdu BMC activation in anaerobic MWB plus rhamnose conditions, suggests that the observed activation of B12 synthesis enzymes does not result in the production of sufficiently high levels of (de novo) B12 to trigger full induction (Figure 3A and Supplementary Table 5).…”

Predominance of Distinct Listeria Innocua and Listeria Monocytogenes in Recurrent Contamination Events at Dairy Processing Facilities

“…Further, atypical strains with deficient rhamnose fermentation have been reported to be attenuated in virulence and have reduced resistance to temperature changes [45]. In contrast, L. monocytogenes serotype 1/2a mutants confer phage-resistance due to a loss of rhamnose.…”

From food to cell: nutrient exploitation strategies of enteropathogens

“…Although the capability to degrade l -rhamnose is present in the genomes of many enteropathogens (), a role of this metabolic pathway in vivo remains to be elucidated. Recently, a novel transcription factor was identified in L. monocytogenes strains associated with foodborne infections and it could be demonstrated that this prfA -like regulator contributes to l -rhamnose utilization (Salazar et al , 2013).…”