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

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 (N2O). We show that marine AOA available in pure culture sustain high ammonia oxidation activity at low M O-2 concentrations, characteristic of suboxic regions of OMZs (<10 mu M O-2), and that atmospheric concentrations of O-2 may inhibit the growth of some environmental populations. We quantify the increasing N2O production by marine AOA with decreasing O-2 tensions, consistent with the plausibility of an AOA contribution to the accumulation of N2O 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.