Determination of Cyanobacterial Nitrogen Fixation : by Acetylene-Reduction Assay (ARA)

Some cyanobacteria, more specifically those of the order Nostocales, have the ability to process nitrogen fixation within specialized cells, namely heterocysts. Heterocysts contain the enzyme complex nitrogenase that is capable of catalyzing the conversion of atmospheric nitrogen to ammonia. The following study will start with an introduction of cyanobacteria, their capability for nitrogen fixation and how the fixed amount of nitrogen can be measured. Then the applied methods are presented including the aim to optimize the ARA by testing the method of David et al. (1980), which attempts to precipitate acetylene by adding ammonical silver nitrate in order to terminate nitrogenase activity, as well as comparing the nitrogen fixation rates of different cyanobacterial strains. The obtained results are then presented and discussed respectively. Finally, a conclusion is given stating the gained findings.