Methanethiol accumulation exacerbates release of N2O during denitrification in estuarine sediments and bacterial cultures

Summary Microbes play critical roles in the biogeochemical cycling of nitrogen and sulfur in aquatic environments. Here we investigated the interaction between the naturally occurring organic sulfur compound methanethiol (MeSH) and the final step of the denitrification pathway, the reduction of nitrous oxide (N2O) to dinitrogen (N2) gas, in sediment slurries from the temperate Douro and Ave estuaries (NW Portugal) and in pure cultures of the marine bacterium Ruegeria pomeroyi. Sediment slurries and cell suspensions were amended with a range of concentrations of either MeSH (0–120 µM) or methionine (0–5 mM), a known precursor of MeSH. MeSH or methionine additions caused N2O to accumulate and this accumulation was linearly related to MeSH concentrations in both coastal sediments (R2 = 0.7–0.9, P