Ammonium and free amino acid uptake by a deep-sea mussel (Bathymodiolus sp., undescribed) containing methanotrophic bacterial symbionts

Abstract

Mussels (Bathymodiolus sp., undescribed) that contain endosymbiotic methanotrophic bacteria were collected from the vicinity of hydrocarbon seeps on the Louisiana Slope of the Gulf of Mexico during September 1989 and 1991. In the presence of methane, these mussels took up ammonium and free amino acids (FAA) but not nitrate. Rates of ammonium uptake ranged from 0.11 to 0.78 μmolg-1 h-1 following initial concentrations of 3.7 to 140.0 μM. The relationship between uptake rate and ammonium concentration exhibited by these mussels appears to be non-linear, apparently differing from the linear kinetics exhibited by algal-invertebrate symbioses. Alanine and glycine were depleted from the medium by symbiotic mussels at rates of 0.10 and 0.07 μmolg-1 h-1 following initial concentrations of 1 μM. Given estimates of rates of carbon fixation and ammonium and FAA levels encountered by the mussels in situ, it is likely that ammonium uptake can meet the nitrogen needs of the association, and that acquisition of carbon and nitrogen from FAA uptake may be an important supplement.