The Ammonia Oxidising Archaeon Nitrosopumilus maritimus Does Not Alter Iodine Oxidation State in Oxic Seawater

We investigate the potential for the globally distributed marine ammonia oxidising archaeon (AOA) Nitrosopumilus maritimus to oxidise iodide (I−), with the aim of identifying a key driver of seawater iodate (IO3−) renewal. Batch cultures of N. maritimus grew well in concentrations of 0.1 to 1 mM NH4+ and from 0.0001 to 1 mM I−. There was near 100% conversion of ammonium to nitrite over an 8-day growth period. No loss of I− or production of IO3− was detected in cultures where I− was added, indicating that N. maritimus is unable to drive I− oxidation under the tested conditions. This contrasts with previous observations of I− oxidation by ammonium oxidising bacteria (AOB). We explore whether differences between the metabolism of AOA and AOB could explain their differing actions on I−. N. maritimus cultures grown with the equivalent IO3− concentrations also showed no reduction in [IO3−]. In addition, the growth of the N. maritimus culture was unaffected by inorganic iodine concentrations over 1000 times higher than in ambient seawater, suggesting a resilience to high iodine. These results suggest that AOA might have very little role in inorganic iodine turnover in the global ocean.