EVIDENCE OF NITRIFICATION ASSOCIATED WITH JELLYFISH

Nitrogen often represents the limiting element for primary production in the surface ocean and its availability is therefore closely linked to ecosystem productivity. Jellyfish excrete inorganic nitrogen in the form of ammonium, the usually preferentially assimilated form of inorganic nitrogen. Here we demonstrate for the first time the potential of jellyfish-associated microbiomes for nitrification, the stepwise oxidation of ammonia via nitrite to nitrate. Incubations in artificial seawater of four species of jellyfish (Aurelia aurita, Chrysaora fulgida, Chrysaora hysoscella and Chrysaora pacifica) show substantial rates of nitrification associated with all three species, however the produced forms of inorganic nitrogen differ. Accumulation of nitrite in incubations with C. fulgida (1.03±0.02 nmol gWW^-1h^-1) indicate the presence of ammonia-oxidizing mircoorganisms, but the absence of nitrite-oxidizing bacteria. A. aurita in contrast appears to harbour both types of nitrifiers, indicated by the accumulation of nitrate (5.43±0.48 nmol gWW^-1h^-1), while C. hysoscella and C. pacifica induce accumulation of both nitrite and nitrate (C. hysoscella: 2.66±0.41 and 10.73±3.26 nmol gWW^-1h^-1; C. pacifica: 2.10±0.14 and 41.61±2.84 nmol gWW^-1h^-1), suggesting uncoupling of the two steps. Our results suggest that nitrifiers are typically associated with jellyfish but that the composition of the nitrifying community varies. This observation is a major progress in our understanding of the role of jellyfish microbiomes in nitrogen cycling.