Nitrogen-fixing growth by nonheterocystous cyanobacterium Plectonema boryanum

Nitrogenase derepresssion, its regulation and metabolic changes associated with diazotrophy in the non-heterocystous cyanobacterium Plectonema boryanum PCC 73110

“…boryanum PCC 73110 synthesized nitrogenase and showed nitrogenase activity in the absence of combined nitrogen (Figs 2, 4). These activities are among the highest reported by other workers using this strain (Stewart & Lex, 1970 Rogerson, 1980; Pearson & Howsley, 1980;Giani & Krumbein, 1986). Since the cultures used were nonsynchronous, development of nitrogenase in all the cells (including those undergoing cell division) and the uniform distribution throughout the cells (Fig.…”

“…However, repeated peaks of alternating nitrogenase activity and oxygen evolution or growth have not been demonstrated. On the other hand, there are conflicting reports of N2 fixation and concomitant growth in Plectonema boryanum (Rogerson, 1980;Pearson & Howsley, 1980;Giani & Krumbein, 1986). Furthermore, virtually no information is available regarding levels of phycoerythrin (PE), GS, nitrate uptake, NR and Rubisco under diazotrophic growth conditions in these cyanobacteria.…”

The Hydrogen Metabolism of Cyanobacteria (Blue‐green Algae)

“…Turning to anoxygenic photosynthesis, although this mode of H, formation is commonplace in photosynthetic bacteria, it is rare in cyanobacteria. It must involve a temporal separation of oxygen and hydrogen formation (Weare & Benemann, 1974;Gallon, 1981), or an inhibition of oxygen formation, usually together with the addition of an assimilable carbon source (Rippka & Stanier, 1978 ;Jones & Bishop, 1976) or some other source of electrons (Peschek, 1 9 7 9~;Belkin & Padan, 1978a, b ;Rogerson, 1980) to allow photosystem I to operate. Such conditions can occur both naturally and by laboratory manipulation.…”

“…Nitrogen-fixing growth of P . boryanum, for example, can occur under both anaerobic (Rogerson, 1980) and aerobic (Pearson & Howsley, 1980) conditions. The provision of DCMU (3-(3,4-dichlorophenyl)-I, I -dimethylurea) to ensure fully anaerobic conditions and the supply of a utilizable carbon source can enhance nitrogenase activity (Rippka & Waterbury, 1977;Rippka & Stanier, 1978).…”

“…It must be remembered that the inhibition of nitrogenase activity by H, is specific to the substrate N,, and hence studies in which C,H, reduction is used to measure nitrogenase activity do not permit any conclusion regarding this question to be made. Circumstantial evidence against significant H, inhibition of N, fixation stems from the ability of P. boryanum to grow under nitrogen-fixing conditions (Weare & Benemann, 1974;Pearson & Howsley, 1980;Rogerson, 1980) even though this cyanobacterium lacks hydrogen-recycling ability under all conditions tested to date (Weare & Benemann, 19-74;. Of great value will be the isolation of hydrogenase-deficient mutants of a heterocystous strain.…”