Diurnal Nitrogenase Modification in the Cyanobacterium Anabaena variabilis*

Abstract

The nitrogen-fixing cyanobacterium Anabaena uariabilis (ATCC 29413) was cultivated as continuous culture under a 12 h : 12 h light-dark cycle. In the light, photosynthetic activity resulted in a continuous increase in cellular glycogen content, followed by an almost complete dissimilation of the polysaccharide during the dark period. Nitrogenase activity, assayed by the acetylene reduction technique, was low at the end of the dark period and increased quickly upon illumination to reach a maximum after 4 to 6 h of light. The activity rapidly declined after darkening the culture. Increase and decrease of activity were accompanied by a change in the electrophoretic mobility of the Fe-protein of nitrogenase (dinitrogenase reductase) indicative of enzyme modification being involved in the diurnal control of nitrogenase activity. Modification and demodification of the Fe-protein were not coupled to the cell cycle since they followed darkening and illumination when the light or dark periods were changed. Addition of fructose increased nitrogenase activity even in darkness and caused demodification of the Fe-protein. Ammonium chloride supplied at the onset of illumination slowed down the increase of nitrogenase activity. A delayed inhibition of the enzyme was accompanied by partial Feprotein modification only. The reaction was completed after transfer to darkness. The function of enzyme modification in maintaining a constant C : N ratio is discussed and a dominating role of carbohydrate supply in this regulation is indicated by the reported findings.

Regulation of nitrogenase activity in relation to the light-dark regime in the filamentous non-heterocystous cyanobacterium Trichodesmium sp. NIBB 1067

“…ADP-ribose attached to one of the two subunits of the Fe-protein inactivates the enzyme, and the modified subunit increases the apparent molecular mass of the Fe-protein by about 1.5 kDa as determined by SDS-PAGE (Gotto & Yoch, 1982;Preston & Ludden, 1982). Similar changes in the apparent molecular mass of the Fe-protein have been observed in cyanobacteria, although the occurrence of ADP-ribosylation has not been demonstrated (Ernst et al, 1990;Reich & Boger, 1989;Smith et al, 1987). Since there are some similarities in the correlation of activity with the change in apparent molecular mass of the Fe-protein between R. rubrum and Trichodesmiurn, nitrogenase activity in Trichodesmium could be regulated by a similar mechanism to that in R. rubrum.…”

“…Oscillation of nitrogenase activity in cells grown under a light-dark regime has been observed for heterocystous (Ernst et al, 1990) and non-heterocystous (Huang et al, 1990;Mitsui et al, 1986;Mullineaux et al, 1981 ;Stal & Krumbein, 1985) cyanobacteria. In non-heterocystous species, nitrogenase activity is high in the dark and becomes low or insignificant in the light.…”

Aerobic nitrogen fixation is confined to a subset of cells in the non‐heterocystous cyanobacterium Symploca PCC 8002

“…Gloeothece (Mullineaux, Gallon & Chaplin, 1981), Cyanothece (Schneegurt et al, 1994) and Oscillatoria (Stal & Heyer, 1987) all separate N # fixation and photosynthesis in time, fixing N # mainly during the dark period of a light\dark cycle. Heterocystous cyanobacteria, which possess cells specialized for N # fixation, confine most of their N # fixation to periods when solar energy or artificial light is available (Griffiths, Gallon & Chaplin, 1987 ;Ernst et al, 1990). This is possible because the N # -fixing heterocysts are deficient in oxygenic photosynthesis and have cell walls that are structurally modified to limit penetration of atmospheric O # (Haselkorn, 1978 ;Carr, 1983 ;Gallon, 1992).…”

Maximum rates of N2 fixation and primary production are out of phase in a developing cyanobacterial bloom in the Baltic Sea

“…The larger form was consistently less abundant than the smaller form, and there was no evidence that the relative concentrations of the two forms varied during the 24-h period of study. It would be premature, therefore, to suggest that the observed fluctuations in nitrogenase activity were related to any shift between different forms of the Fe protein, as has been suggested for Anabaena variabilis (Ernst et al 1990), Oscillatoria limosa (Villbrandt et al 1992), and Trichodesmium (Zehr et al 1993).…”