Resumen:
β-Lactam resistance (βLR) in Streptococcus pneumoniae is due to
mutations in penicillin-binding proteins (PBPs) PBP1a, PBP2x, and
PBP2b, enzymes involved in cell wall synthesis and division. We
have previously described a relationship between pbp2b mutations
and morphological alterations, growth retardation, a high fitness
cost, unusual simultaneous septa and FtsZ delocalization. The
clinical βLR strains harboring these pbp2b mutations showed no
morphological abnormalities, but in a laboratory strain, the
association of pbp mutated genes in double and triple pbp mutants
caused partial and complete compensatory effects on cell division
and fitness. By optical microscopy, subpopulations of pbp2b cells
showed bacillar and coccoid (as wild-type strain) shapes. However,
by electron microscopy, these coccoid-shape cells exhibited
different defects, such as incomplete and atypical septum formation
and positioning, intracellular structures and frequent asymmetrical
divisions. The double pbp2b/2x mutant showed inner cell wall
accumulation, but the triple pbp mutant compensated these
morphological alterations. In addition, the localization pattern of
the PBP2b*-GFP fusion protein in wild-type and pbp2b mutant cells
was consistent with a cell cycle deregulation. These results
suggested that PBP2b is involved in essential processes related to
cell shape determination and cell division.