Abstract
The permeability coefficeint for NH3 through bacterial membranes was determined to be around 2 × 10−3 cm·s−1. This value was used to calculate the outward diffusion of NH3 from intracellular pools and the energy costs for reabsorption as NH4 +. For an N2-fixing continuous culture of Klebsiella pneumoniae an energy expenditure of around 4 ATP per NH3 produced was calculated, thus increasing significantly the energy requirement for N2 fixation in vivo.