The penicillin-binding proteins (PBPs) are enzymes involved in cell wall synthesis and cell division in Streptococcus pneumoniae. We have previously described that Cp1015 strain containing pbp2b mutations (from clinical strains that confer â-lactam resistance) showed a pneumococcal subpopulation with bacillary shape, atypical septum formation and positioning, frequent asymmetrical divisions, and a PBP2B and FtsZ delocalization. These results suggested that PBP2b is involved in essential processes related to cell shape determination and cell division.
By two-hybrid assays, we revealed that PBP2b interacted with different proteins, such as ErzA, MreC, RodA and FtsA, which were involved in cell division, but in other bacteria with different cell division mechanisms to S. pneumoniae. To determine the contribution of these proteins in pneumococcal morphogenesis, we constructed the mreC, rodA, ftsA and erzA mutants by insertion-duplication mutagenesis using the pEVP3 vector. These mutants displayed small colonies, fitness and morphological alterations. We also detected cell-wall biosynthesis alterations by vancomycin-fluorescein staining in all mutants. These results suggested that ErzA, MreC, RodA and FtsA could contribute, together with PBP2b, to determine the pneumococcal cell shape of S. pneumoniae.
