Peptidoglycan synthesis and its fine chemical composition in dividing and not dividing Klebsiella pneumoniae cocci

Peptidoglycan synthesis and its fine chemical composition were studied in dividing and in non-dividing Klebsiella pneumoniae cocci and compared with rods. The beta-lactam mecillinam, a specific inhibitor of lateral wall elongation which causes rod-to-sphere transition in rods, showed 50% inhibition of the peptidoglycan in normal rods of the parent Mir A12 only if added at an early stage of the cell cycle and no effect if added later or during septation. In the rods of the mutant Mir M7, mecillinam was shown to inhibit 50% of peptidoglycan synthesis until rods become cocci, and thereafter to be absolutely devoid of effects. On the contrary, piperacillin, a specific inhibitor of septum formation, was active on all strains regardless of their cell shape, only if added at 20 and removed at 40 min of the cell cycle. As regards the analysis of peptidoglycan fine chemical composition, bacteria dividing as cocci showed alterations in the muropeptide composition consisting in a 50-fold increase in the tetramer family. This alteration was not seen in the cocci that did not divide as such. These results confirm our previous claim that septum formation and lateral wall elongation are mutually exclusive in normal rods and that septum formation requires the synthesis of a peptidoglycan of different chemical composition.