Interactions between anaerobic ammonium and sulfur-oxidizing bacteria in a laboratory scale model system.

Fixed nitrogen is released by anaerobic ammonium oxidation (anammox) and/or denitrification from (marine) ecosystems. Nitrite, the terminal electron acceptor of the anammox process, occurs in nature at very low concentrations and is produced via (micro)aerobic oxidation of ammonium or nitrate reduction. The coupling of sulfide-dependent denitrification to anammox is particularly interesting because besides hydrogen, sulfide is the most important reductant at the chemocline of anoxic marine basins and is abundant within sediments. Although at μM concentrations, sulfide may be toxic and inhibiting anammox activity, a denitrifying microorganism could convert sulfide and nitrate at sufficiently high rates to allow anammox bacteria to stay active despite an influx of sulfide. To test this hypothesis, a laboratory scale model system containing a co-culture of anammox bacteria and the autotrophic denitrifier Sulfurimonas denitrificans DSM1251 was started. Complementary techniques revealed that the gammaproteobacterial Sedimenticola sp. took over the intended role of Su. denitrificans. A stable coculture of anammox bacteria and Sedimenticola sp. consumed sulfide, nitrate, ammonium and CO2 . Anammox bacteria contributed 65-75% to the nitrogen loss from the reactor. The cooperation between anammox and sulfide-dependent denitrification may play a significant role in environments where sulfur cycling is active and where actual sulfide concentrations stay below μM range.