Figure 5.

The range of R_r/o yielding reasonable (1 nM–1 mM) intracellular metabolite concentrations. Results are shown only for electron carriers that allow near-thermodynamic fractionations at low csSRR. Columns and rows show electron carriers for APS and SO₃²⁻ reduction, respectively. White space indicates combinations of R_r/o that produce unreasonable intracellular metabolite concentrations over some or all of the range of csSRR accessed in culture experiments (0.1 to 125 fmol H₂S per cell per day). Colored contours indicate the magnitude of net isotope fractionation at a csSRR of 0.1 fmol H₂S per cell per day and with values of K_M for APS at Apr shown in the lower right corner of each panel. Other K_M were at their default values (Supplementary Table S5). When the same electron carrier is involved in both APS and SO₃²⁻ reduction (on the diagonal), the possible range of R_r/o is further constrained to be on the solid grey line.