Fungal denitrification revisited - Recent advancements and future opportunities

Fungi play a key role in the nitrogen cycle. Diverse fungi are known to reduce nitrate or nitrite to gaseous nitrogen oxides such as nitric oxide, nitrous oxide (N2O), and dinitrogen via denitrification or co-denitrification (microbially mediated nitrosation), and to ammonium via ammonia fermentation (fungal dissimilatory nitrate reduction to ammonium). These processes could significantly contribute to the emission of N2O from soils and the removal of nitrogen from nitrate and nitrite-contaminated environments. However, fungal N2O production may not be necessarily related to their denitrification activity sensu stricto (i.e., reduction of nitrate or nitrite to gaseous N oxides for respiration): N2O can be produced by partially abiotic processes. Therefore, fungi that can reduce nitrate or nitrite to N2O should not be called denitrifying fungi instantaneously. Experiments should be carefully conducted to better discriminate fungal denitrification, co-denitrification, and chemo-denitrification. Various analytical tools have been developed and applied to clarify fungal denitrification and other nitrate/nitrite reduction processes, including the substrate-induced respiration-inhibition method, stable isotope analyses, and culture-dependent and -independent molecular and genomic approaches. In this mini-review, we overview fungal denitrification and other nitrate/nitrite reduction processes, discuss their environmental impacts, summarize recent advancements in the methods to study fungal denitrification, and provide insights on future research opportunities.

Automated summary

Fungi play a key role in the nitrogen cycle by reducing nitrate and nitrite to gaseous nitrogen oxides. However, fungal N2O production may not be solely related to denitrification, and experiments should be carefully conducted to discriminate between different nitrate/nitrite reduction processes. Various analytical tools have been developed to study fungal denitrification, offering insights for future research opportunities.