NO and N₂O transformations of diverse fungi in hypoxia: evidence for anaerobic respiration only in Fusarium strains

Abstract

Fungal denitrification is claimed to produce nonnegligible amounts of N 2 O in soils, but few tested species have shown significant activity. We hypothesized that denitrifying fungi would be found among those with assimilatory nitrate reductase, and tested 20 such batch cultures for their respiratory metabolism, including two positive controls, Fusarium oxysporum and Fusarium lichenicola, throughout the transition from oxic to anoxic conditions in media supplemented with NO − 2 . Enzymatic reduction of NO − 2 (NIR) and NO (NOR) was assessed by correcting measured NO-and N 2 O-kinetics for abiotic NO-and N 2 O-production (sterile controls). Significant anaerobic respiration was only confirmed for the positive controls and for two of three Fusarium solani cultures. The NO kinetics in six cultures showed NIR but not NOR activity, observed through the accumulation of NO. Others had NOR but not NIR activity, thus reducing abiotically produced NO to N 2 O. The presence of candidate genes (nirK and p450nor) was confirmed in the positive controls, but not in some of the NO or N 2 O accumulating cultures. Based on our results, we conclude that only the Fusarium cultures were able to sustain anaerobic respiration and produced low amounts of N 2 O as a response to an abiotic NO production from the medium.

Comparing modified substrate-induced respiration with selective inhibition (SIRIN) and N<sub>2</sub>O isotope approaches to estimate fungal contribution to denitrification in three arable soils under anoxic conditions

“…2 ), nitric oxide (NO) and N 2 O (Knowles, 1982). For a long time, it was believed that solely bacteria are involved in N 2 O formation during denitrification (Firestone and Davidson, 1989); however, several fungi are also capable of denitrification (Bollag and Tung, 1972;Shoun et al, 1992).…”

Gross Ammonification and Nitrification Rates in Soil Amended with Natural and NH4-Enriched Chabazite Zeolite and Nitrification Inhibitor DMPP

“…Nitrification is normally favoured under wellaerated conditions and a good NH 4 + supply [35]. Under oxygen limiting conditions, NO 3 − can be used by several microbes as a terminal electron acceptor and is converted to the gaseous forms N 2 O and N 2 [36]. The complete process involves the enzymes nitrate reductase (Nar), nitrite reductase (Nir), nitric oxide reductase (Nor), and nitrous oxide reductase (Nos) [37].…”

Isolation of cold‐adapted nitrate‐reducing fungi that have potential to increase nitrate removal in woodchip bioreactors

“…It is important to note, however, that co-denitrification has been criticized as the microbially mediated nitrosation (Spott et al 2011), in which NO 2or NO formed by biotic reaction (e.g., nitrate reduction) can abiotically react with other N species (e.g., amines) to form N-N bonding (e.g., N 2 , N 2 O). Therefore, microbes that can reduce NO 3to NO 2may also produce gaseous N species (e.g., Mania et al, 2014;Keuschnig et al, 2020).…”