Rates of metabolic activity in marine coastal sediment-hosted microbial communities. (A) Inferred rates of sulfate reduction by individual single cells encoding for sulfate reduction genes in the incubated sediment extracts, calculated from the RSG-fluorescence calibration versus estimated cell diameter inferred from forward scatter size-calibrated beads (methods for calculation described in [23, 24]). Each cell directed encoded for key genes involved in sulfate reduction in the SAG (dsrAB and aprAB). The specific incubation experiment conditions for each SAG and cell is indicated with symbol shapes, and the taxonomy is indicated with symbol colors. Per-cell sulfate reduction rates ranged from 0.02 to 4.65 fmol cell⁻¹ hr⁻¹. (B) Transcript quantities of key genes involved in sulfate reduction (sat, dsrAB, aprAB; mean RPKM) and RSG fluorescence values from the SAG genomes the transcripts map to. The colors indicate taxonomy per panel A, and transcript source sample is indicated with a circle (0% oxygen with added laminarin) or triangle (25% oxygen with added laminarin). (C) Average rates of sulfide production per cell for sulfate reduction-capable cells of the Chloroflexota and Desulfobacterota phyla across RSG-stained samples. (D) Total RSG fluorescence of gated particles that represent “cell-like” particles in sediment slurry with different incubation additions, incubated at 10°C for 24 h. Total fluorescence was calculated by summing the green fluorescence of each cell in a sample, normalized to volume, as previously done in [24]. Overall, the data show that laminarin stimulates sulfate respiration activity.