Chitinase Expression in Listeria monocytogenes Is Influenced by lmo0327, Which Encodes an InternalinLike Protein

Abstract

The chitinolytic system of Listeria monocytogenes thus far comprises two chitinases, ChiA and ChiB, and a lytic polysaccharide monooxygenase, Lmo2467. The role of the system in the bacterium appears to be pleiotropic, as besides mediating hydrolysis of chitin, the second most ubiquitous carbohydrate in nature, the chitinases have been deemed important for colonization of unicellular moulds, as well as mammalian hosts. In order to identify additional components of the chitinolytic system, we screened a transposon mutant library for mutants exhibiting impaired chitin hydrolysis. The screening yielded a mutant with a transposon insertion in a locus corresponding to lmo0327 of the EGD-e strain. lmo0327 encodes a large (1349 aa) cell-wall associated protein that has been proposed to possess murein hydrolase activity. Single inactivation of lmo0327, as well as of lmo0325 that codes for a putative transcriptional regulator functionally related to lmo0327, led to an almost complete abolishment of chitinolytic activity. The effect could be traced at the transcriptional level, as both chiA and chiB transcripts were dramatically decreased in the lmo0327 mutant. In accordance with that, we could barely detect ChiA and ChiB in the culture supernatants of the mutant strain. Our results provide new information regarding the function of the lmo0325-lmo0327 locus in L. monocytogenes and link it to the expression of chitinolytic activity.Importance: Many bacteria from terrestrial and marine environments express chitinase activities enabling them to utilize chitin as the sole source of carbon and nitrogen. Interestingly, several bacterial chitinases may also be involved in host pathogenesis. For example, in the important food borne pathogen Listeria monocytogenes, the chitinases ChiA and ChiB, and the lytic polysaccharide monooxygenase Lmo2467 are implicated in chitin assimilation, but also act as virulence factors during infection of mammalian hosts. Therefore, it is important to identify their regulators and induction cues in order to understand how the different roles of the chitinolytic system are controlled and mediated. Here we provide evidence for the importance of lmo0327 and lmo0325, encoding a putative internalin/autolysin and a putative transcriptional activator, respectively, in the efficient expression of chitinase activity in L. monocytogenes, and thereby provide new information regarding the function of the lmo0325-lmo0327 locus.