ANAEROBIC NITRATE REDUCTION TO AMMONIUM IN 2 STRAINS ISOLATED FROM COSTAL MARINE SEDIMENT - A DISSIMILATORY PATHWAY

A total of 28 nitrate-reducing bacteria were isolated from marine sedi ment (Mediterranean coast of France) in which dissimilatory reduction of nitrate to ammonium (DRNA) was estimated as 80% of the overall nitr ate consumption. Thirteen isolates were considered as denitrifiers and ten as dissimilatory ammonium producers. N-15 ammonium production fro m N-15 nitrate by an Enterobacter sp. and a Vibrio sp., the predominan t bacteria involved in nitrate ammonification in marine sediment, was characterized in pure culture studies. For both strains studied, nitra te-limited culture (1 mM) produced ammonium as the main product of nit rate reduction (> 90%) while in the presence of 10 mM nitrate, nitrite was accumulated in the spent media and ammonia production was less ef ficient. Concomitantly with the dissimilation of nitrate to nitrite an d ammonium the molar yield of growth on glucose increased. Metabolic p roducts of glucose were investigated under different growth conditions . Under anaerobic conditions without nitrate, ethanol was formed as th e main product; in the presence of nitrate, ethanol disappeared and ac etate increased concomitantly with an increased amount of ammonium. Th ese results indicate that nitrite reduction to ammonium allows NAD reg eneration and ATP synthesis through acetate formation, instead of etha nol formation which was favoured in the absence of nitrate.