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Appl Environ Microbiol. 1982 May; 43(5): 1076-1079

Effect of Sulfide on Nitrogen Fixation in a Stream Sediment-Water System

¹ Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
² Department of Microbiology, Macdonald Campus of McGill University, Ste Anne de Bellevue, Québec, Canada H9X 1C0

ABSTRACT

Nitrogen fixation (C₂H₂ reduction) in a sediment-water system was studied under anaerobic incubation conditions. Sodium sulfide at low concentrations stimulated activity, with a twofold increase in C₂H₄ production occurring in the presence of 8 µmol of S^2– per ml of stream water. Sodium sulfide at concentrations of 16 µmol of S^2– per ml or greater inhibited nitrogen fixation, with 64 µmol of S^2– per ml being completely inhibitory. Sulfide at levels of 16 µmol/ml or above inhibited CO₂ production, and the degree of inhibition increased with increasing concentration of sulfide. Titanium (III) citrate (used to modify Eh levels) stimulated both nitrogen fixation and CO₂ production, but could not duplicate, at any concentration tested, the twofold increase in nitrogen fixation caused by 8 µmol of S^2– per ml. Sulfide additions caused pH changes in the sediment, and when the sediment was adjusted and maintained at pH 7.0 all concentrations of sulfide inhibited nitrogen fixation activity. From considerations of the redox equilibria of H₂, H₂S, and other sulfur species at various pH values, it appeared that H₂S was the toxic entity and that HS^– was less toxic. The observed stimulation of activity was apparently due to a pH change coupled with the concurrent production of HS^– from H₂S.