Setting of the Circadian N2-Fixing Rhythm of the Prokaryotic Synechococcus sp. RF-1 while Its nif Gene Is Repressed

Huang, Tan-Chi; Chou, Wing‐Ming

doi:10.1104/pp.96.1.324

Cited by 22 publications

(12 citation statements)

References 9 publications

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“…The freshwater Synechococcus strain RF-1 differs from the strains reported here in its slower doubling time and the production of more extracellular slime. These cells also adhere to glassware, which can be prevented by replacing the normal medium with conditioned medium (15). This strain is also more difficult to plate and does not appear to grow photoheterotrophically.…”

Section: Discussionmentioning

confidence: 99%

“…It is reported to exhibit a circadian rhythm for N2 fixation when grown under a normal light-dark regimen (15,18,19). When cultures were grown with alternating light and dark periods of 14 h of each, 12 h of each, or 10 of each, they demonstrated an endogenous N2-fixing rhythm with a free-running period of about 24 h for at least four cycles (15). We are interested in investigating this phenomenon further and believe that Cyanothece strains BH63 and BH68 represent better experimental organisms for such studies.…”

Section: Discussionmentioning

confidence: 99%

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Unicellular, aerobic nitrogen-fixing cyanobacteria of the genus Cyanothece

et al. 1993

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Two marine, unicellular aerobic nitrogen-fixing cyanobacteria, Cyanothece strain BH63 and Cyanothece strain BH68, were isolated from the intertidal sands of the Texas Gulf coast in enrichment conditions designed to favor rapid growth. By cell morphology, ultrastructure, a GC content of 40%c, and aerobic nitrogen fitation ability, these strains were assigned to the genus Cyanothece. These strains can use molecular nitrogen as the sole nitrogen source and are capable of photoheterotrophic growth in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and glycerol. The strains demonstrated a doubling time of 10 to 14 h in the presence of nitrate and 16 to 20 h under nitrogen-fixing conditions. Rapid growth of nitrogen-fixing cultures can be obtained in continuous light even when the cultures are continuously shaken or bubbled with air. Under 12-h alternating light and dark cycles, the aerobic nitrogenase activity was confined to the dark phase. The typical rates of aerobic nitrogenase activity in Cyanothece strains BH63 and BH68 were 1,140 and 1,097 nmol of C2H2 reduced per mg (dry weight) per h, respectively, and nitrogenase activity was stimulated twofold by light. Ultrastructural observations revealed that numerous inclusion granules formed between the photosynthetic membranes in cells grown under nitrogen-fixing conditions. These Cyanothece strains possess many characteristics that make them particularly attractive for a detailed analysis of the interaction of nitrogen fixation and photosynthesis in an aerobic diazotroph.In all nitrogen-fixing organisms, the nitrogen fixation process is carried out by nitrogenase, an extremely oxygensensitive enzyme. Microorganisms have developed various strategies to protect their nitrogenase from oxygen inhibition (2, 5, 6). Among the nitrogen-fixing microorganisms, the cyanobacteria occupy a unique position because these are the only oxygenic photosynthetic organisms capable of nitrogen fixation under aerobic conditions (13). Nitrogen fixation has been reported for all three major morphological groups of cyanobacteria: heterocystous filamentous, nonheterocystous filamentous, and unicellular forms (5, 13). The oxygen protection mechanisms employed by these organisms vary considerably. In the heterocystous filamentous strains, about 5 to 10% of the cells undergo morphological differentiation into specialized cells called heterocysts under nitrogen-fixing conditions (13,49). In this arrangement, nitrogen fixation and photosynthetic oxygen evolution are spatially separated, so that oxygenic photosynthesis takes place in vegetative cells and nitrogen fixation occurs in heterocysts. The fixed nitrogen from these cells is exported to the neighboring vegetative cells, and the reductant for nitrogen fixation is imported from the vegetative cells (5, 49).There are many genera of nonheterocystous cyanobacteria, both filamentous and unicellular, that are capable of nitrogen fixation. The nonheterocystous filamentous forms have been placed in the genera Trichodesmium, Oscillatoria, an...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Unicellular, aerobic nitrogen-fixing cyanobacteria of the genus Cyanothece

et al. 1993

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“…It is known that circadian nitrogenase activity is controlled at the transcription level and that the m f gene is repressed in the presence of nitrate (Huang and Chou 1991). In order to determine which proteins, other than nitrogenase, are also controlled by the oscillator in Synechococcus RF-1, the polypeptides synthesized in the presence of nitrate (BG-11 medium) labeled with [35S]methionine were examined by SDS-gel electrophoresis.…”

Section: Comparison Of the Circadian Rhythms Induced By Tempera-mentioning

confidence: 99%

Biological clock in the prokaryote Synechococcus RF-1

Huang

Chen

Pen

et al. 1994

Planta

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The prokaryote Synechococcus RF-1 exhibits circadian rhythms of nitrogen fixation and leucine uptake after being entrained in a diurnal light/dark regimen. The rhythms can also be established by small temperature changes, in either a raised-or a lowered-temperature cycle, within the growth-permissive range. At the biochemical level, the circadian oscillator in Synechococcus RF-1 controls, in addition to the nitrogenase, the synthesis rate at which more than ten polypeptides are synthesized. At the physiological and the biochemical levels, the overt rhythms have fixed phase relationships, though the phase is dependant on the particular induction stimuli. A "clock" consisting of a molecular complex which can respond differentially to different induction conditions is hypothesized.

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“…Therefore, a culture of Synechococctls RF-1 growing in nitrate-containing medium does not have nitrogenase activity. When a culture growing in a nitrate-containing medium is exposed to a diurnal L/D regimen, a circadian nitrogenase activity rhythm manifests itself after the culture is transferred to a nitrate-free medium and is incubated in constant illumination (Huang & Chou, 1991). The results indicate that the circadian nitrogenfixing rhythm of Synechococcns RF-1 can be induced while the nfgene is repressed.…”

Section: The Circadian Rhythms In Synechococcus Rf-1 At the Biochemicmentioning

confidence: 92%