Effect of Nitrogen on Yield Using Bioenergetics Theory

Abstract

The form of nitrogen influences the yield of microorganisms from a given amount of substrate. Previous work on calculating yields from thermodynamic principles is modified to give a correct account for the form of nitrogen. Nitrogen in the reduced form of ammonia contributes energy toward cell synthesis while the more highly oxidized forms of nitrogen require an expenditure of energy. In addition, the electron equivalency of cells changes depending on the form of nitrogen available to the microorganisms. These principles are incorporated into two approaches that yield equivalent results to formulate the overall reaction stoichiometry for substrate, nitrogen source, cells, and other products based on bioenergetics. An example is given where the change of nitrogen source from nitrate to ammonia results in an increase in cell yield of 29%.