Nitrogen isotope fractionation during the reduction of NO3− to NH4+ by Desulfovibrio sp.

Desulfovibrio reduce NO3−to NH4+ via a dissimilatory pathway. In 21 days, four strains of Desulfovibrio reduced 36–48% of the available NO3− to ammonium. During this reductive process extensive nitrogen isotope fractionation occurred: the product NH4+ was enriched in 15N in the initial sample, then became enriched in 14N to a minimum value at approximately 20–25% reaction, and then became isotopically heavier as the reaction proceeded.