ALTERNATIVE AND CYCLIC APPEARANCE OF H-2 AND O-2 PHOTOPRODUCTION ACTIVITIES UNDER NONGROWING CONDITIONS IN AN AEROBIC NITROGEN-FIXING UNICELLULAR CYANOBACTERIUM SYNECHOCOCCUS SP

With synchronously grown cells of an aerobic unicellular marine cyanob acterium Synechococcus sp. Miami BG 043511, changes in the activities of anoxygenic, nitrogenase-dependent hydrogen photoproduction and oxyg en photoevolution were measured under nongrowing hydrogen production c onditions. Interestingly, synchronously grown cells, incubated in ligh t under an argon atmosphere, exhibited cyclic changes in the activity of nitrogenase-catalyzed hydrogen production for approximately 20- to 25-h intervals. Cyclic photosynthetic oxygen production activity also appeared in approximately the same intervals. However, changes in hydr ogen production and oxygen production activities were inversely correl ated and temporally separated. Stepwise accumulation of hydrogen in cl osed vessels was also observed in approximately 24-h cycles in these n on-growing cells. These observations in non-growing cells suggest that this unicellular aerobic, nitrogen-fixing cyanobacterium may have an endogenous system to control the exhibition of cyclic rhythms, in addi tion to the previously studied cell cycle-oriented system. Expression and switching between these two systems may be related to the sufficie ncy or insufficiency of nitrogen growth nutrients. The possibility of the existence of a common control factor of the two systems involving glycogen is also discussed.