Fig. 4: Isotope- and genome-informed enrichment and physiology kinetics of putative F-SOHDs.
From: Versatile nitrate-respiring heterotrophs are previously concealed contributors to sulfur cycle
a A custom strategy used for the long-term enrichment of F-SOHDs. Estuary sediments (referred to START) served as the inoculum. Given that F-SOHDs can couple denitrification with OM oxidation with or without sulfide as an additional electron donor, the medium altered between the absence and presence of sulfide, iterating for 67 cycles over a duration of 460 days. A 152-day sequencing batch bioreactor was operated to pre-enrich the sediments with relatively high biomass. CMD represents the incubation condition wherein inorganic carbon, nitrate, and sulfide are supplied. Within each dilution transfer cycle, the enrichments generated from HED incubation were introduced into CMD incubation to test chemolithoautotrophic potential. Enrichments demonstrating positive responses to the CMD condition were discarded, while those displaying unfavorable response were inoculated to the next cycle. ENR represents the ultimate enrichments (ENR_C4 and ENR_U2) dominated by F-SOHDs. b, c Reaction kinetics of ENR_C4 enrichment with different substrates provided. In the Co + N and Co + N + S treatments, OM serves as the sole carbon source, whereas the Ci + N + S treatment relies on inorganic carbon provision. Dissolved sulfide and fresh nitrate are provided upon the depletion of nitrate and nitrite at 63 h. d, e Net increase rates of cell numbers of ENR_C4 and ENR_U2 under different incubation conditions (two-tailed unpaired Student’s t test with 95% confidence intervals). Data from three biological replicates are presented as mean values ± SEM. Source data are provided as a Source Data file.
