VISUALIZATION OF PENICILLIN-BINDING PROTEINS DURING SPORULATION OF STREPTOMYCES-GRISEUS

We used fluorescein-tagged beta-lactam antibiotics to visualize penici llin-binding proteins (PBPs) in sporulating cultures of Streptomyces g riseus. Six PBPs were identified in membranes prepared from growing an d sporulating cultures. The binding activity of an 85-kDa PBP increase d fourfold by 10 to 12 h of sporulation, at which time the sporulation septa were formed. Cefoxitin inhibited the interaction of the fluores cein-tagged antibiotics with the 85-kDa PBP and also prevented septum formation during sporulation but not during vegetative growth. The 85- kDa PBP, which was the predominant PBP in membranes of cells that were undergoing septation, preferentially bound fluorescein-6-aminopenicil lanic acid (Flu-APA). Fluorescence microscopy showed that the sporulat ion septa were specifically labeled by Flu-APA; this interaction was b locked by prior exposure of the cells to cefoxitin at a concentration that interfered with septation. We hypothesize that the 85-kDa PBP is involved in septum formation during sporulation of S. griseus.