Cell Division Inhibition in Salmonella typhimurium Histidine-Constitutive Strains: an ftsI-Like Defect in the Presence of Wild-Type Penicillin-Binding Protein 3 Levels

Histidine-constitutive (His(c)) strains of Salmonella typhimurium undergo cell division inhibition in the presence of high concentrations of a metabolizable carbon source. Filaments formed by His(c) strains show constrictions and contain evenly spaced nucleoids, suggesting a defect in septum formation. Inhibitors of penicillin-binding protein 3 (PBP3) induce a filamentation pattern identical to that of His(c) strains. However, the His(c) septation defect is caused neither by reduced PBP3 synthesis nor by reduced PBP3 activity. Gross modifications of peptidoglycan composition are also ruled out. d-Cycloserine, an inhibitor of the soluble pathway producing peptidoglycan precursors, causes phenotypic suppression of filamentation, suggesting that the septation defect of His(c) strains may be caused by scarcity of PBP3 substrate.