Timing of Mucopeptide and Phospholipid Synthesis in Sporulating Bacillus megaterium

During sporulation, the processes of septation and envelopment create a double membraned structure (the forespore) which is destined to become the spore. In this paper we present biochemical data to support the hypothesis that septation and envelopment result from the continued synthesis of plasma membrane in the absence of cell wall synthesis. Using a double auxotroph of Bacillus megaterium requiring both diaminopimelic acid and lysine, it has been possible to follow mucopeptide formation unambiguously by measuring incorporation of radioactive diaminopimelic acid. Membrane synthesis has been determined by measuring the incorporation of (14C)-ethanolamine or (14C)-acetate into phospholipid. Upon glucose exhaustion and the initiation of sporulation, vegetative cell mucopeptide synthesis ceased for a period of 3 hours. Approximately 1 hour after the cessation of mucopeptide synthesis, an accelerated rate of phospholipid synthesis was observed that continued for about 3 hours. This biochemical data was correlated with morphological changes observed during the initial stages of sporulation.