Methylamine,an inhibitor of ammonium oxidation and chemoautotrophic growth in the marine nitrifying bacteriumNitrosococcus oceanus

Methylamine (CH₃NH₃⁺) appeared to utilize the same transport mechanism as ammonium (NH₄⁺) to enter cells ofNitrosococcus oceanus. Methylamine uptake did not show clear evidence of saturable kinetics and was not fully saturated at 20 mM. Assimilated CH₃NH₃⁺ was not incorporated into macromolecular constituents, but inhibited rates of nitrification, chemoautotrophic CO₂ fixation and growth. The degree of inhibition was dependent on the relative concentrations of NH₄⁺ and CH₃NH₃⁺. Rates of CO₂ fixation and growth were inhibited four times more than the rate of nitrification.