Septation sporogener und asporogener Bacillus megaterium‐Zellen während des Übergangs zu Stickstoff‐ und Kohlenstoff‐hunger

Abstract

AbstractFirst, the kinetics and frequency of sporulation of two Bacillus megaterium strains were determined after transition to nitrogen starvation. As the formation of the spore septum started at 1 hour after the shift, the initiation of sporogenesis was similar to that observed earlier in carbohydrate limited cultures. But later processes of sporulation were retarded and partly inhibited.From these strains two sporulation defective mutants were isolated. In ammonia‐, resp. glucose‐ or arabinose‐limited cultures cell division of the sporogenic and asporogenic strains was studied electronmicroscopically. Samples were taken from 2 generations before the transition to the stationary growth phase (t0) through 3 hours after the shift.Three types of division behaviour were observed during the transition to nitrogen‐(N) or carbon‐(C)‐starvation: The initiation of division was inhibited already 1 ‐ 2 generations before cessation of net growth. In average, about 70% of all visibly initiated division septa were completed by t0 or shortly after that time. This type was expressed in all sp+‐cultures and in the N‐limited sp−‐populations. Initiation of septum formation was stimulated 1 ‐ 2 generations before t0 in sp−‐strains under C‐limitation. About 80% of all initiated septa were completed, if citrate was absent. The completion of the division septum was completely blocked independent of whether initiation was stimulated or inhibited. This inhibition of late division processes occurred with sp−‐strains under C‐ or N‐limitation in glucose‐citrate medium. From these results it is concluded that the metabolism of sp+‐ and sp−‐strains differs already 1 ‐ 2 generations before t0. Concerning factors controlling division early sporulating cells resemble N‐starved cells, independent of the composition of the medium. Initiation of division is at least influenced by the ratio of catabolic to anabolic reactions in a cell. Initiation and completion of the septum are separately controlled steps of the division process, but probably not of the spore septum formation.