Fig. 5: Impact of F-SOHDs on biogeochemical cycling and nitrous oxide (N2O) emission.
From: Versatile nitrate-respiring heterotrophs are previously concealed contributors to sulfur cycle
a Sulfide removal in different laboratory cultures under OM-rich and OM-limited conditions. HD is a sediment enrichment culture containing conventional heterotrophic denitrifiers that do not engage in sulfur oxidation. CD is a pure culture of the chemolithoautotrophic sulfur-oxidizing denitrifier Thiobacillus denitrificans ATCC 25259. The ENR_U2 and ENR_C4 are two enrichments dominated by F-SOHDs with incomplete and complete sulfur oxidation capacities, respectively. The three different microbial communities were established by combining the HD culture with the CD T. denitrificans in ratios of 3:1 (CE_H, high ratio), 1:1 (CE_E, equal ratio), and 1:3 (CE_L, low ratio). Both ENR_U2 and ENR_C4 experiments were replicated three times under OM-limited conditions, and the final concentration of sulfide were consistently below detection limits. b Contribution of electrons derived from sulfide (green boxes) and OM (dashed lines) to denitrification process in OM-rich cultures. The calculation is conducted under the assumption that nitrate is fully reduced to dinitrogen gas. c Contribution of electrons derived from sulfide (green boxes) and OM (dashed lines) to denitrification in OM-limited cultures. The light blue boxes indicate the completion extent of denitrification (i.e., the percent of electrons produced as a function of the total electrons needed to completely reduce nitrate to dinitrogen). Gray boxes represent the completion extent of denitrification in the absence of OM. d OM metabolism by various laboratory cultures under OM-rich and OM-limited conditions. The comparison of OM consumption is conducted under the assumption that total electron donors in each laboratory culture are sufficient for supporting complete denitrification e, f Emission of N2O and N2 by the enrichment culture of conventional heterotrophic denitrifiers in the presence or absence of sulfide under OM-rich conditions. Percentages are shown by nitrogen atoms normalized to the initial concentration of nitrate. g N2O emission by various laboratory cultures under OM-rich and OM-limited conditions. All experimental data from three biological replicates are presented as mean values ± SEM (two-tailed unpaired Student’s t test with 95% confidence intervals). Source data are provided as a Source Data file.
