Evaluation of O-antigen inactivation on Pla activity and virulence of Yersinia pseudotuberculosis harbouring the pPla plasmid

Abstract

Yersinia pestis is a species that emerged recently from Yersinia pseudotuberculosis and gained an exceptional pathogenicity potential. Among the major genetic differences between the plague bacillus and its ancestor is the acquisition of the pPla plasmid, which has been associated with the increased virulence of Y. pestis. In a previous study, introduction of pPla into Y. pseudotuberculosis did not lead to any modification of the virulence of the host bacterium. However, it was subsequently demonstrated that the presence of smooth lipopolysaccharide (LPS) inhibits the activity of Pla. In this study, pPla was introduced into a Y. pseudotuberculosis strain expressing smooth LPS, and into a variant in which a mutation that abrogates the formation of O-antigen (O-Ag) repeats (as in natural isolates of Y. pestis) was generated. It was found that in both strains, Pla was synthesized, exported to the bacterial membrane and processed as in Y. pestis. However, the ability of Pla to activate plasminogen was weak and observed only at 37 °C in the smooth strain, while this activity was similar to that of Y. pestis and expressed at both 28 and 37 °C in the O-Ag mutant strain. Similarly, Pla-mediated inactivation of the antiprotease α 2-antiplasmin was not detected in the smooth Y. pseudotuberculosis strain grown at 28 °C, but was expressed at both temperatures in the O-Ag mutant strain. Despite the more efficient activity of Pla, the Y. pseudotuberculosis O-Ag mutant strain exhibited a lower pathogenicity upon subcutaneous infection of mice. The results thus indicate that, although abrogation of O side chain synthesis in a Y. pseudotuberculosis strain harbouring pPla potentiates the two proteolytic activities of Pla, this is not sufficient to confer to Y. pseudotuberculosis a higher pathogenicity potential. These results also suggest that acquisition of pPla may not have been sufficient to confer an immediate higher pathogenic potential to the ancestor Y. pestis strain.

Direct Transcriptional Control of the Plasminogen Activator Gene of Yersinia pestis by the Cyclic AMP Receptor Protein

“…One explanation for the reduction in Pla activity displayed by crp and cyaA mutants is that these strains produce less Pla. Alternatively, at least when heterologously expressed in other bacteria, Pla proteolytic activity is affected by changes to the bacterial cell envelope (27). This presents the possibility that production of Pla remains unchanged but its activity is altered by cAMP-Crp-mediated changes in gene expression that ultimately alter the cell envelope.…”

Capsular Antigen Fraction 1 and Pla Modulate the Susceptibility of Yersinia pestis to Pulmonary Antimicrobial Peptides Such as Cathelicidin

“…For example, the Salmonella omptin PgtE, unlike the Escherichia coli omptin OmpT, cleaves plasminogen to plasmin well, albeit 1,000 times less efficiently than Pla does (23,32,56). Access of plasminogen to omptins such as Pla and PgtE is inhibited by the addition and lengthening of the LPS O-chain repeats, respectively (34,46). Y. pestis has a rough-type LPS that lacks an O-specific chain (54), resulting in efficient plasminogen activation by Pla.…”

Delineation and Analysis of Chromosomal Regions Specifying Yersinia pestis

“…Although the horizontally acquired pPla plasmid plays a major role in the virulence of most Y. pestis isolates, the facts that it is dispensable in some strains (35,49,63) and that its introduction into Y. pseudotuberculosis is not accompanied by an increase in virulence (34,42) clearly indicate that other factors are required. One of them has been shown to be the Ypf⌽ filamentous phage (13), but other Y. pestis-acquired chromosomal loci may have also played a role in this gain of virulence.…”

“…Therefore, the stage of the infectious process during which pPla exerts its activity remains unclear. Furthermore, acquisition of pPla is not sufficient to account by itself for the dramatic rise in virulence of Y. pestis, because there are natural isolates of Y. pestis that lack pPla and still are highly virulent to mice (63) or guinea pigs (49) after subcutaneous injection (49,63), and introduction of pPla in Y. pseudotuberculosis does not increase its virulence in mice (34,42).…”