Nitrous oxide (N₂O) synthesis by the freshwater cyanobacterium Microcystis aeruginosa

Abstract

Abstract. Pure cultures of the freshwater cyanobacterium Microcystis aeruginosa synthesized nitrous oxide (N2O) when supplied with nitrite (NO2-) in darkness (198.9 nmol g-DW−1 h−1 after 24 h) and illumination (163.1 nmol g-DW−1 h−1 after 24 h), whereas N2O production was negligible in abiotic controls supplied with NO2- and in cultures deprived of exogenous nitrogen. N2O production was also positively correlated to the initial NO2- and M. aeruginosa concentrations but was low to negligible when nitrate (NO3-) and ammonium (NH4+) were supplied as the sole exogenous N source instead of NO2-. A protein database search revealed that M. aeruginosa possesses protein homologous to eukaryotic microalgae enzymes known to catalyze the successive reduction of NO2- into nitric oxide (NO) and N2O. Our laboratory study is the first demonstration that M. aeruginosa possesses the ability to synthesize N2O. As M. aeruginosa is a bloom-forming cyanobacterium found globally, further research (including field monitoring) is now needed to establish the significance of N2O synthesis by M. aeruginosa under relevant conditions (especially in terms of N supply). Further work is also needed to confirm the biochemical pathway and potential function of this synthesis.

Sub-daily Variations in Nitrous Oxide Fluxes from the Littoral Zone of a Temperate Eutrophic Lake

“…The higher concentrations imply that an N 2 O source was present on the lake surface, as some types of cyanobacteria and green algae produce N 2 O (Weathers, 1984;Fabisik et al, 2023).…”

Are Microalgae New Players in Nitrous Oxide Emissions from Eutrophic Aquatic Environments?

“…The role of this enzyme has not been described yet, but its presence suggests another potential pathway for NO synthesis from NO 2 − in the mitochondria. Bellido-Pedraza et al [27] estimated that nearly one third of the 100 photosynthetic microorganisms described in genomic databases contain at least one of the proteins involved in N 2 O synthesis in Chlamydomonas (NirK, CYP55, FLVs, and HCP), including the widely distributed and dominant cyanobacterium in freshwater ecosystems Microcystis aeruginosa [18]. There is, therefore, clear evidence for the existence of several broadly distributed N 2 O synthesis pathways in microalgae.…”

“…Challenging this view, eutrophic aquatic environments are characterized by the abundance of microalgae whose growth is not necessarily linked (or linearly correlated) to the N inputs received and whose ability to produce N 2 O has now been clearly demonstrated [12][13][14][15][16][17]. Microalgae species from the Bacillariophyta, Chlorophyta, and Cyanobacteria have indeed been shown to synthesize N 2 O in the laboratory [13,18] and significant N 2 O emissions have been reported during microalgae cultivation outdoors [12,19,20].…”

Seasonal variability of nitrous oxide concentrations and emissions in a temperate estuary

“…This respiration in turn is determined by remineralization of algal material from the upstream river that is transported to and respired within the port region (Schroeder, 1997;Kerner, 2000;Schöl et al, 2014), linking estuarine N 2 O production to river eutrophication. Fabisik et al (2023) showed that algae could additionally contribute to N 2 O production. In the Elbe, fresh organic matter from the river with low C/N values as well as high PN and PC contents entered the estuary.…”