The reduction of nitrates to nitrites, dinitrogen oxide (nitrous oxide) or dinitrogen catalysed by microoganisms, e.g. facultative aerobic soil bacteria under anaerobic conditions.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 151 (https://doi.org/10.1351/pac199264010143)