Serogroup-Specific Interaction of Neisseria meningitidis Capsular Polysaccharide with Host Cell Microtubules and Effects on Tubulin Polymerization

We have previously shown that during late stages of the infectious process, serogroup B meningococci (MenB) are able to escape the phagosome ofin vitro -infected human epithelial cells. They then multiply in the cytosolic environment and spread intracellularly and to surrounding cells by exploiting the microtubule cytoskeleton, as suggested by results of infections in the presence of microtubule inhibitors and evidence of nanotubes connecting neighboring cells. In this study, by using microtubule binding assays with purified microtubule asters and bundles and microtubule bundles synthesizedin vitro , we demonstrate that the MenB capsule directly mediates the interaction between bacteria and microtubules. The direct interaction between the microtubules and the MenB capsular polysaccharide was confirmed by coimmunoprecipitation experiments. Unexpectedly, serogroup C meningococci (MenC), which have a capsular polysaccharide that differs from that of MenB only by its anomeric linkage, α(2→9) instead of α(2→8), were not able to interact with the microtubules, and the lack of interaction was not due to capsular polysaccharideO -acetylation that takes place in most MenC strains but not in MenB strains. Moreover, we demonstrate that the MenB capsular polysaccharide inhibits tubulin polymerizationin vitro . Thus, at variance with MenC, MenB may interfere with microtubule dynamics during cell infection.