Various microorganisms responsible for denitrification in soil

Denitrification is a key process in the nitrogen cycle that reduces nitrate and nitrite to nitric oxide, nitrous oxide (N2O), and dinitrogen gas. Denitrification is also a key reaction involved in nitrogen loss from agricultural soils and emission of the greenhouse gas N2O. In recent years, significant findings have been reported regarding the diversity, function, and ecology of the microorganisms responsible for denitrification. This review provides an overview of the ecological and functional characteristics of various microorganisms involved in soil denitrification, as well as technologies for controlling denitrification. Genomic and metagenomic analyses of the denitrification enzymes nitrite reductase (Nir) and nitric oxide reductase (Nor) in soil revealed that denitrifying bacteria exhibit niche partitioning based on soil properties. In addition to canonical denitrifying bacteria, non-denitrifying N2O-reducing bacteria exist in the soil, and three clades of the nitrous oxide reductase gene (nosZ) have been identified. Furthermore, many denitrifying bacteria possess only partial sets of denitrification enzymes, suggesting that denitrification is driven by modular processes in the environment. Meanwhile, fungi have been known to be capable of denitrification. Effective primers were designed to detect the fungal denitrification enzyme genes NirK and cytochrome P450 nitric oxide reductase (P450nor). Metagenomic and isotopomer analyses with these primers demonstrated that fungal denitrification functioned as a major pathway in some soil environments. Denitrifying activity has also been found among microorganisms involved in the carbon, sulfur, and iron cycles, indicating the coupling of nitrogen and other biogeochemical cycles. Although actinomycetes and archaea have been shown to possess denitrification metabolic pathways, further investigation is needed to determine their actual contributions to soil denitrification capacity. The development of diverse technologies for controlling denitrification has been promoted. Approaches utilizing N2O-reducing bacteria and soybean rhizobia with enhanced Nos activity have successfully mitigated N2O at the field level. Furthermore, N2O mitigation has been demonstrated by improving soil physical properties with biochar. The use of chemicals to inhibit denitrification specifically has been demonstrated at the laboratory level.