ISSN:
1432-072X
Keywords:
Plectonema boryanum
;
N2-fixation
;
Exponential growth
;
Microaerobiosis
;
Light
;
Pigments
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Strains of filamentous, non-heterocystous cyanobacteria from the Pasteur Culture Collection (PCC), able to synthesize nitrogenase under anaerobic test conditions, were tested for growth with N2 as sole nitrogen source at low O2 partial pressure (less than 0.05%). Plectonema boryanum (PCC 73110) exhibited exponential growth under these conditions. This capacity was restricted to light intensities not exceeding 500 lux. Growth rates were 0.014/h at 200 and 0.023 at 500 lux and similar to those of anaerobic and aerobic control cultures with nitrate as N-source. For N2-fixing cultures incubated at 200 and 500 lux, acetylene reduction rates were 4–8 and 5–14 nmol C2H4 per mg protein per min, respectively. The ratio of phycocyanine to chlorophyll was higher (200 lux) or slightly reduced (500 lux) in N2-fixing cultures as compared to control cultures with nitrate as N-source. On the basis of epifluorescence microscopy and microfluorimetry, no differences in pigment contents were found between individual cells or filaments of N2-fixing cultures. Also no noteworthy differences were observed between the pycobiliprotein composition of individual cells in N2 fixing cultures as compared to nitrate-grown controls. Thus the observed exponential growth of P. boryanum at low light intensities implies simultaneous nitrogen fixation and oxygenic photosynthesis. Additional continuous culture experiments showed that N2-fixing exponential growth was dependent on O2 partial pressures lower than 0.2–0.4%. The other strains tested (PCC 6412, 6602, 7403, 7104) did not grow under such conditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00443655
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