ABSTRACT

Nitrogen is one of the most important elements for organisms. It may account for up to 10% of the dry weight of biomass. Nitrogen occurs in amino acids-the building blocks of polypeptides, enzymes, and other proteins-but also in the nucleic acids (DNA and RNA), in the cell wall, and in chlorophyll. In all these compounds, nitrogen is present in its reduced (−3) state. Hence, organisms living at the expense of oxidized nitrogen such as dinitrogen, nitrate, or nitrite must reduce it before this nitrogen can be assimilated and used for the synthesis of structural cell material.