Influence of oxygen availability on the activities of ammonia‐oxidizing archaea

Summary Recent studies point to the importance of oxygen (O 2 ) in controlling the distribution and activity of marine ammonia‐oxidizing archaea (AOA), one of the most abundant prokaryotes in the ocean. The AOA are associated with regions of low O 2 tension in oceanic oxygen minimum zones (OMZs), and O 2 availability is suggested to influence their production of the ozone‐depleting greenhouse gas nitrous oxide (N 2 O). We show that marine AOA available in pure culture sustain high ammonia oxidation activity at low μM O 2 concentrations, characteristic of suboxic regions of OMZs (<10 µM O 2 ), and that atmospheric concentrations of O 2 may inhibit the growth of some environmental populations. We quantify the increasing N 2 O production by marine AOA with decreasing O 2 tensions, consistent with the plausibility of an AOA contribution to the accumulation of N 2 O at the oxic‐anoxic redox boundaries of OMZs. Variable sensitivity to peroxide also suggests that endogenous or exogenous reactive oxygen species are of importance in determining the environmental distribution of some populations.