Identification of EloR (Spr1851) as a regulator of cell elongation in Streptococcus pneumoniae

5 years ago

Identification of EloR (Spr1851) as a regulator of cell elongation in Streptococcus pneumoniae

Leiv Sigve Håvarstein, Anja Ruud Winther, Cyril Alexander Frantzen, Daniel Straume, Morten Kjos, Gro Anita Stamsås

In a screen for mutations suppressing the lethal loss of PBP2b in Streptococcus pneumoniae we identified Spr1851 (named EloR), a cytoplasmic protein of unknown function whose inactivation removed the requirement for PBP2b as well as RodA. It follows from this that EloR and the two elongasome proteins must be part of the same functional network. This network also includes StkP, as this serine/threonine kinase phosphorylates EloR on threonine 89 (T89). We found that ΔeloR cells, and cells expressing the phosphoablative form of EloR (EloRT89A), are significantly shorter than wild-type cells. Furthermore, the phosphomimetic form of EloR (EloRT89E) is not tolerated unless the cell in addition acquires a truncated MreC or non-functional RodZ protein. By itself, truncation of MreC as well as inactivation of RodZ gives rise to less elongated cells, demonstrating that the stress exerted by the phosphomimetic form of EloR is relieved by suppressor mutations that reduce or abolish the activity of the elongasome. Of note, it was also found that loss of elongasome activity caused by truncation of MreC elicits increased StkP-mediated phosphorylation of EloR. Together, the results support a model in which phosphorylation of EloR stimulates cell elongation, while dephosphorylation has an inhibitory effect. Cell division and elongation are major cellular processes that are tightly regulated during the bacterial cell cycle. Here we identify and characterize a cytoplasmic protein, EloR, that is part of a regulatory pathway controlling cell elongation in Streptococcus pneumoniae. We provide evidence that the non-phosphorylated form of EloR negatively affects cell elongation, while the phosphorylated form has a stimulatory effect. As EloR is conserved among Gram-positive bacteria, our results have significance beyond the genus Streptococcus.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/mmi.13748