Simultaneous sulfate and nitrate reduction in coastal sediments

Abstract

The oscillating redox conditions that characterize coastal sandy sediments foster microbial communities capable of respiring oxygen and nitrate simultaneously, thereby increasing the potential for organic matter remineralization, nitrogen (N)-loss and emissions of the greenhouse gas nitrous oxide. It is unknown to what extent these conditions also lead to overlaps between dissimilatory nitrate and sulfate respiration. Here, we show that sulfate and nitrate respiration co-occur in the surface sediments of an intertidal sand flat. Furthermore, we found strong correlations between dissimilatory nitrite reduction to ammonium (DNRA) and sulfate reduction rates. Until now, the nitrogen and sulfur cycles were assumed to be mainly linked in marine sediments by the activity of nitrate-reducing sulfide oxidisers. However, transcriptomic analyses revealed that the functional marker gene for DNRA (nrfA) was more associated with microorganisms known to reduce sulfate rather than oxidise sulfide. Our results suggest that when nitrate is supplied to the sediment community upon tidal inundation, part of the sulfate reducing community may switch respiratory strategy to DNRA. Therefore increases in sulfate reduction rate in-situ may result in enhanced DNRA and reduced denitrification rates. Intriguingly, the shift from denitrification to DNRA did not influence the amount of N2O produced by the denitrifying community. Our results imply that microorganisms classically considered as sulfate reducers control the potential for DNRA within coastal sediments when redox conditions oscillate and therefore retain ammonium that would otherwise be removed by denitrification, exacerbating eutrophication.

Sulfate as an Alternative Electron Acceptor: A Potential Strategy to Mitigate N2O Emissions in Upland Arable Soils

“…Although N2O reduction may have been impaired, N2O emissions were still lower than the controls due to diminished N2O generation. This observation aligns with findings from SO4 2 ⁻-rich environments (e.g., coastal wetlands and riverbed soils) where NO3⁻ consumption processes, such as denitrification and dissimilatory nitrate/nitrite reduction to ammonium, are inhibited, reducing N2O production 40,41 . Additionally, in the metabolic pathways of sulfate-reducing bacteria, SO4 2 ⁻ serves as an EA, being reduced to hydrogen sulfide (H2S).…”

Metagenomics and Stable Isotopes Uncover the Augmented Sulfide-Driven Autotrophic Denitrification in a Seasonally Hypoxic, Sulfate-Abundant Reservoir

“…Subtropical reservoirs are susceptible to seasonal hypoxia due to stratification, leading to diverse patterns in the response of benthic nitrate reduction to oxygen under various hypoxic scenarios. − Given that oxygen levels in some of these seasonally hypoxic reservoirs fall below the denitrification and sulfate reduction thresholds, these waters emerge as potential hotspots for coupled nitrogen and sulfur cycling. The biogeochemical significance of NO 3 – utilization by sulfur-oxidizing bacteria has been widely acknowledged in marine sediments, freshwater sediments, , and groundwater systems to date. Despite this importance, research on coupled N–S cycling in seasonally hypoxic reservoirs remains notably scarce compared to studies conducted in oceans and estuaries, particularly in the water column of reservoirs.…”