Untitled

Abstract

The daily cycle of nitrogenase expression in the marine filamentous nonheterocystous cyanobacterium Trichodesmium spp. is controlled by a circadian rhythm. We evaluated the rhythm of two key photosynthesis genes, psbA of photosystem II and psaA of photosystem I, in Trichodesmium sp. IMS 101 using the 3 criteria for an endogenous rhythm. The transcript abundance of psbA and psaA transcripts oscillated with a period of ca. 24 h under a 12 h light/12 h dark regime. At 24 degrees C and 28 degrees C the cyclic pattern of transcript abundance was maintained for at least 58 h under constant light conditions, whereas the periods were about 24 h at 24 degrees C, and 26-30 h at the higher temperature. The cycles of psbA and psaA gene expression were entrained using light-dark cues. Transcription of nifHDK was initiated prior to the light period, followed by psbA and finally psaA. There was a 90 degrees (6 h) phase difference between the net accumulation of nifHDK and psbA transcripts, as well as between that of psbA and psaA transcripts. Results of inhibitor experiments indicated that psbA and psaA transcription was regulated differently by initiation and degradation during the light period. Short-term changes of light conditions resulted in significant effects on psbA transcription and nitrogenase activity, but had less of an effect on psaA and nifHDK transcription.

Diurnal expression of hetR and diazocyte development in the filamentous non-heterocystous cyanobacterium Trichodesmium erythraeum

“…4). This finding may explain the presence of the nitrogenase protein during the night (Zehr et al, 1993;Fredriksson & Bergman, 1995;Chen et al, 1998), and further confirms that the nitrogenase protein abundance is reflected in the nifH transcription pattern .…”

Synthesis and proteolytic degradation of nitrogenase in cultures of the unicellular cyanobacterium Gloeothece strain ATCC 27152

“…In this organism, the Fe-protein can be detected more or less throughout a diurnal illumination cycle but a putatively inactive form predominates during the light period, when no nitrogenase activity can be detected, and is converted to an assumed active form prior to the appearance of activity (Villbrandt et at., 1992). A similar correlation between the onset of N, fixation and the appearance of an assumed active form of the Fe-protein exists in the unusual non-heterocystous cyanobacterium Trichodesmiurn (Chen et al, 1998;Ohki et al, 1992;Zehr et al, 1993), which fixes N, during the day, and in the heterocystous cyanobacterium Anabaena variabilis (Ernst et al, 1990).…”

“…strain ATCC 51142 (Colon-Lopez et aE., 1997) but differs from all of the other non-heterocystous cyanobacteria so far examined, none of which show complete turnover of nitrogenase when grown under alternating light and darkness. In all of these cyanobacteria, both the MoFeprotein and the Fe-protein of nitrogenase could be detected in cells throughout the illumination cycle (Chen et al, 1998;Ohki et af., 1992;Villbrandt et al, 1992;Zehr et al, 1993).…”

Origin and evolution of circadian clock genes in prokaryotes

“…In cyanobacteria, the clock genes were shown to be involved in the regulation of nitrogen fixation (32), cell division (33), and other metabolic processes (4,34). Furthermore, reproductive fitness of cyanobacteria increases when the endogenous clock and the temporal environmental cycle are strictly synchronized (35).…”