Lon protease- and temperature-dependent activity of a lysis cassette located in the insecticidal island of Yersinia enterocolitica

The Yersinia genus comprises pathogens that are able to adapt to an environmental life cycle stage as well as to mammals. Yersinia enterocolitica strain W22703 exhibits both insecticidal and nematocidal activity conferred by the tripartite toxin complex (Tc) that is encoded on the 19 kb pathogenicity island Tc-PAIYe. All tc genes follow a strict temperature regulation in that they are silenced at 37°C, but activated at lower temperatures. Four highly-conserved phage-related genes, located within the Tc-PAIYe, were recently demonstrated to encode a biologically functional holin-endolysin gene cassette that lyses its own host W22703 at 37°C (1). Conditions transcriptionally activating the cassette are yet unknown. In contrast to E. coli, the overproduction of holin and endolysin did not result in cell lysis of strain W22703 15°C. When the holin-endolysin genes were overexpressed at 15°C in four Y. enterocolitica biovars and in four other Yersinia spp., a heterogenous pattern of phenotypes was observed, ranging from lysis resistance of a biovar 1A strain to a complete growth arrest of a Y. kristensenii strain. To decipher the molecular mechanism underlying this temperature-dependent lysis, we constructed a Lon protease negative mutant of W22703 in which overexpression of the lysis cassette leads to cell death at 15°C. Overexpressed endolysin exhibited a high proteolytic susceptibility in strain W22703, but remained stable in strain W22703 Δlon or in Y. pseudotuberculosis. Although artificial overexpression was applied here, the data indicate that Lon protease plays a role in the control of the temperature-dependent lysis in Y. enterocolitica W22703.