Abstract
Several genes of the eut, pdu, and cob/cbi operons are responsible for the metabolism of ethanolamine (EA) and 1,2-propanediol (PD) and are essential during the pathogenic lifecycles of various enteric pathogens. Studies concerning EA and PD metabolism have primarily focused on bacterial genera from the family Enterobacteriaceae, especially the genus Salmonella. Listeria monocytogenes is a member of the Firmicutes phylum and is the causative agent of the rare but highly fatal foodborne disease listeriosis. The eut, pdu, and cob/cbi operons are organized as a single large locus collectively referred to as the cobalamin-dependent gene cluster (CDGC). The CDGC is well conserved in L. monocytogenes; however, functional characterization of the genes in this cluster and how they may contribute to Listeria virulence and stress tolerance in food production environments is highly limited. Previous work suggests that the degradation pathway of PD is essential for L. monocytogenes establishment in the gastrointestinal tract. In contrast, EA metabolism may be more important during intracellular replication. Other studies indicate that the CDGC is utilized when L. monocytogenes is exposed to food and food production relevant stress conditions. Perhaps most noteworthy, L. monocytogenes exhibits attenuated growth at cold temperatures when a key EA utilization pathway gene was deleted. This review aims to summarize the current knowledge of these pathways in L. monocytogenes and their significance in virulence and stress tolerance, especially considering recent developments.
Highlights
Foodborne pathogens must adapt to various stress conditions to survive in food production and host environments
Several transcriptomic studies show that the cobalamin-dependent gene cluster (CDGC) is differentially expressed during food and food production environment relevant stress conditions, functional characterization of how CDGC mechanisms may contribute to L. monocytogenes stress tolerance is, to the best of our knowledge, currently unavailable
One important aspect of CDGC that should be addressed in future research is to identify whether EA catabolism may have an effect on the host immune system and commensal bacteria of the intestine
Summary
Foodborne pathogens must adapt to various stress conditions to survive in food production and host environments. The capacity to metabolize alternative substrates for energy is imperative for the survival of pathogens when more efficient nutrients are unavailable. Such environments include – among others – the nutrient-limited conditions within the phagosomes of macrophages. Cobalamin in Listeria monocytogenes of various enteric pathogens, including Salmonella enterica, Enterococcus faecalis, Escherichia coli, and Listeria monocytogenes. Enzymes required for the metabolism of PD and EA are dependent on cobalamin (vitamin B12) derivatives as cofactors. Studies concerning the functional characterization of EA and PD metabolic genes and how they contribute to virulence have been, for the most part, conducted in Salmonella, E. coli, and Enterococcus. The ability to utilize EA and PD has been demonstrated in other distantly related genera, including Mycobacterium, Corynebacterium, Lactococcus, and Listeria as well as nonpathogenic bacteria (Nandedkar, 1974; Blackwell et al, 1976; Hartmans and Bont, 1986; Rodionov et al, 2003; Xue et al, 2008; Tsoy et al, 2009; Kutzner et al, 2016; Zeng et al, 2019)
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