|The effect of oxygen concentration and temperature on nitrogenase activity in the heterocystous cyanobacterium Fischerella sp.|In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322; e-ISSN 2045-2322, meer
Heterocysts are differentiated cells formed by some filamentous, diazotrophic (dinitrogen-fixing)cyanobacteria. The heterocyst is the site of dinitrogen fixation providing the oxygen-sensitivenitrogenase with a low-oxygen environment. The diffusion of air into the heterocyst is a compromisebetween the maximum influx of dinitrogen gas while oxygen is kept sufficiently low to allownitrogenase activity. This investigation tested the hypothesis that the heterocyst is capable ofcontrolling the influx of air. Here, the thermophilic heterocystous cyanobacterium Fischerella sp.was analysed for the effects of oxygen concentration and temperature on nitrogenase activity. Darknitrogenase activity is directly related to aerobic respiration and was therefore used as a measure ofthe influx of oxygen into the heterocyst. Above 30% O2, the influx of oxygen was proportional to itsexternal concentration. Below this concentration, the influx of oxygen was higher than expected fromthe external concentration. A higher or lower temperature also triggered the heterocyst to increase ordecrease, respectively, dark nitrogenase activity while the external concentration of oxygen was keptconstant. A higher dark nitrogenase activity requires a higher rate of respiration and therefore a higherflux of oxygen. Hence, the heterocyst of Fischerella sp. is capable of controlling the influx of air.