Nitrification by Marine Bacteria in Low Concentrations of Substrate and Oxygen1

Chemoautotrophic nitrifying bacteria, isolated from open‐ocean waters, oxidized low concentrations of substrate (5 µ g‐atom NH 3 ‐N or 20 µ g‐atom NO 2 − ‐N/liter) in liquid medium containing less than 0.1 ml of oxygen/liter and in solid medium under 0.002 atm of oxygen. Carbon assimilations for three nitrifying bacteria were higher in 0.002 than in 0.2 atm of oxygen. More carbon was assimilated per unit of substrate oxidized in low than in high concentrations of oxygen. In deeper, oxygen‐poor waters of some oceans, high concentrations of nitrite may arise from ammonia oxidation.