Competence enhances adherence of pneumococcus by exposing virulence factors on the cell surface.

What is it about?

Competence in Streptococcus pneumoniae allows this gram-positive bacterium to uptake and integrate DNA, but it also enhances virulence, i.e., its ability to cause disease, by exposing key surface factors that increase host adherence. Competent pneumococci produce fratricins like CbpD that kill noncompetent sibling cells. CbpD binds to key components of the pneumococcal cell wall while the immunity protein ComM protects competent bacteria. We found that LytR is vital for the formation of crucial structural polymers, wall teichoic acids, during competence and together with ComM, is necessary for immunity to fratricide. This study also shows that the virulence factors PspA and PspC become more exposed during competence in a CbpD dependant manner. These findings suggest that activation of competence is crucial for increased surface exposure of CBPs and host adherence.

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Photo by CDC on Unsplash

Photo by CDC on Unsplash

Why is it important?

This study shows that at the heart of immunity towards lysis by CbpD lies ComM, which works in concert with LytR to provide optimal immunity towards CbpD. We propose a model in which the flux of TA from LTA increases towards WTA during competence development by the upregulation of comM and lytR. The study showed that both PspA and PspC are surface-exposed mainly at the midcell, suggesting that the competence-dependent remodeling of the cell wall leads to increased surface exposure of CBPs. We speculate that cell surface remodeling via CbpD, ComM and LytR could be a reason why competence development is switched on during infection, as it can help bacteria better adhere or evade the host’s immune system.

Perspectives