Effects of sulfide on the activity of the ammonia-oxidizing archaeon Nitrosopumilus maritimus SCM1

Abstract

Ammonia-oxidizing archaea (AOA) are frequently found in oxygen-depleted marine environments with permanent or temporal presence of sulfide (HS-). However, it remains unexplored how sulfide affects the activity of ammonia-oxidizing archaea. We studied the capability of Nitrosopumilus maritimus SCM1 to oxidize ammonia when exposed to HS-. Ammonia oxidation remained active even after exposure to sulfidic spikes in the lower micromolar range, albeit at reduced rates compared to the absence of HS-. However, 90 {micro}M HS- completely inhibited ammonia oxidation. We found no evidence of NO-dismutation under oxygen depletion and presence of HS- (20 {micro}M): the formation of O2, N2O and N2 did not occur. All in all, we confirmed ammonia oxidation in N. maritimus SCM1 under oxic conditions after sulfide additions, but no evidence of NO-dismutation under sulfidic conditions. Our findings suggest that AOA can recover ammonia-oxidation activity after oxygen re-exposure in regions with periodic sulfide accumulation. However, in permanently sulfidic areas, ammonia oxidation recovery seems unlikely, as NO-dismutation does not appear to be a viable mechanism.