ABSTRACT
As a major component of all living cells, nitrogen (N) is a fundamental element in the functioning of biological systems. Under N-limited conditions, certain prokaryotic organisms are able to convert atmospheric N2 gas to ammonium a biologically-available N form, through the process of biological N fi xation (Howarth et al. 1988a;b). The process of N fi xation is catalyzed by the enzyme nitrogenase, which is only produced in specifi c prokaryotes including several genera of archaea, bacteria, and cyanobacteria. Cyanobacteria are a class of organisms exhibiting both algal morphologies and distinct bacterial features (Vymazal 1995).
