The Chitinolytic Activity ofListeria monocytogenesEGD Is Regulated by Carbohydrates but Also by the Virulence Regulator PrfA

Abstract

Chitin, an insoluble polymer of N-acetyl-D-glucosamine (GlcNAc), is one of the most abundant carbohydrate polymers in marine and terrestrial environments. Chitin hydrolysis by Listeria monocytogenes depends on two chitinase-encoding genes, chiA and chiB, and the aim of this study was to investigate their regulation. Chitin induces the expression of both chitinases in late exponential growth phase, and chiA but not chiB is furthermore induced by the monomer GlcNAc. Furthermore, their expression is subjected to catabolite control. Chitinases expressed by bacterial pathogens have proven to be important not only for nutrient acquisition and environmental survival but also for infecting animals and humans. Interestingly, the central L. monocytogenes virulence gene regulator, PrfA, is required for the chitinolytic phenotype, as chitinase activity was significantly reduced in prfA mutant cells compared to its level in wild-type cells. In agreement with this, Northern blot analysis showed that the amounts of chiA and chiB transcripts upon induction by chitin were significantly lower in the prfA mutant than in the wild type. The chitinolytic activity and chiA and chiB expression were reduced in the absence of the sigB gene, indicating that B is also important for the production of chitinases. The chiA, chiB, and chiA chiB mutants were not impaired for in vitro adhesion and invasion in epithelial cell lines, but the chiA chiB double mutant showed less survival ability in a chitin-enriched medium. The regulation of chitinolytic activity in L. monocytogenes is complex, and taken together, the results indicate that the biological role of this activity may not be limited to the external environment.

Genomic Potential for Polysaccharide Deconstruction in Bacteria

“…The high prevalence of strains (e.g., Vibrio [42] and Serratia [43] strains) with the potential for chitin degradation highlights chitin as a key resource across ecosystems (i.e., marine and soil ecosystems) (44,45). However, chitinolytic activity is known to be involved in other ecologically relevant pathways, such as pathogenicity (i.e., Listeria strains [46]) and antifungal activity (i.e., Collimonas strains [47]). On average, the lack of potential for chitin processing is observed in clusters of relatives with an average 16S rRNA similarity of 96.1%.…”

Microdiversity of extracellular enzyme genes among sequenced prokaryotic genomes

“…While a high proportion of CHI-positive genotypes (73.75%) were also positive for NAG, we detected potential for CHI production without the potential for NAG production in a few groups within the Firmicutes phylum ( Figure 3). For these strains, CHI production may be primarily involved in virulence (Larsen et al, 2010) or biofilm formation (Tirumalai and Prakash, 2011) instead of resource acquisition. Alternatively, we may not have identified all NAG-positive genotypes in our analysis.…”

Bacterial chitinases and chitin-binding proteins as virulence factors

“…However, the ability of the Legionella pneumophila mutants to survive in macrophage cell cultures is similar to that of the wild-type. This is also the case for Listeria monocytogenes mutants infecting epithelial and macrophage cell cultures (Chaudhuri et al, 2010;DebRoy et al, 2006;Larsen et al, 2010), despite the notion of enhanced intracellular chitinase transcription in macrophages (Mraheil et al, 2011). The in vivo virulence effects of chitinases might not be limited to bacteria, as the trypanosomatid protozoan pathogen, Leishmania mexicana, produces a chitinase that contributes to formation of lesions in a mouse model as well as promoting survival in host macrophage cells (Joshi et al, 2005).…”

“…A Northern blot study demonstrated that the central Listeria monocytogenes virulence regulators PrfA and sB significantly increase transcription of the two chitinase genes chiA and chiB in this organism (Larsen et al, 2010). However, the overall evaluation of the role of Listeria monocytogenes chitinases as virulence factors is complicated by the fact that the expression of both enzymes is also induced by chitin, while only expression of chiA and not chiB is induced by GlcNAc (Larsen et al, 2010).…”

“…There is an increasing amount of direct or indirect evidence suggesting that some chitinases and CBPs additionally serve as virulence factors for bacterial pathogens during infection. Examples include chitinases from Legionella pneumophila (DebRoy et al, 2006), Listeria monocytogenes (Chaudhuri et al, 2010;Larsen et al, 2010) and Salmonella enterica serovar Typhimurium (S. Typhimurium) (Larsen et al, 2011) as well as a CBP from Vibrio cholerae (Kirn et al, 2005). A summary of cell culture/in vivo indications of this role is presented in Tables 1 and 2.…”