Mineralization of organic nitrogen and carbon (fish food) added to anoxic sediment microcosms: role of sulphate reduction

Substrate (fish food) was added to gas-tight bags containing sediment, with and without molybdate. Amino-nitrogen (amino-N) was measured by high-performance liquid chromatography. The oxidation of 3 representative '"C-labelled amino acids (glutamic acid, alanine and arginine) was measured and the mean decay rate constant was used to calculate turnover rates of amino-N. Concentrations of dissolved organic nitrogen, dissolved organic carbon, total inorganic carbon and ammonium were measured during 28 d of incubation. Inhibition of sulphate-reducing activity gave a 4.2-fold decrease in the rate of ammonium production and a 4.5-fold decrease in the rate of amino acid turnover. These results suggest an active participation of sulphate-reducing bacteria in amino acid oxidation.