nondenitrifying

Nondenitrifying describes organisms or microbial processes that do not perform denitrification, the microbial reduction of nitrate to nitrogen gases. Denitrification involves a sequential set of enzymes that convert nitrate to nitrite, then to nitric oxide, nitrous oxide, and finally dinitrogen gas. Nondenitrifying organisms may lack one or more of the enzymes required for this complete pathway or may regulate these genes such that denitrification is not carried out under the prevailing conditions.

Nondenitrifiers can still participate in other nitrogen transformations. Some reduce nitrate only to nitrite, or to ammonium via dissimilatory nitrate reduction to ammonium (DNRA). Others assimilate nitrate into biomass, or participate in separate processes such as nitrification (oxidation of ammonia to nitrate) or ammonification. In ecological and metagenomic studies, the term helps distinguish communities containing complete denitrifiers from those containing organisms that perform other nitrogen-cycle steps or only partial reductions.

Implications for ecosystems include effects on nitrogen retention and loss. Denitrification is a key pathway for removing fixed nitrogen from soils and waters as gaseous N2 or N2O, while nondenitrifying members can influence nitrate accumulation or participate in alternative transformations depending on environmental conditions such as oxygen, carbon availability, and nitrate concentration. Researchers identify denitrifiers through genetic markers (for example, nirK/S and nosZ) and often categorize community members as denitrifying or nondenitrifying to interpret nitrogen cycling dynamics.