Fig. 9

Assessment of supernatant toxicity in Bioassay 3. Fresh cells were inoculated in bioreactor liquid (0, 5, 10, 20, 40, and 75 vol%) in Bioassay 3a. A Gas data for each of the treatments (n = 2). The top shows the O₂ concentration (µmol vial⁻¹) while the bottom shows the cumulative N₂ concentration (µmol N₂-N vial⁻¹). B Initial electron flow rate (fmol e⁻ cell⁻¹ h⁻¹) estimated for each of the treatments in Bioassay 3a, corrected for individual sampling time for each vial, assuming a linear increase in rate during the time (1.7 h) from the first to the second headspace sampling. C Bioassay 3b investigated the toxicity of Fe²⁺ and Fe³⁺. The average N₂ production rate 10–34 h after injection of Fe²⁺/Fe³⁺ was calculated for each Fe concentration and plotted against the concentrations. Since [S] > > K_m both for glucose and nitrate, the inhibition coefficient (K_I, i.e. the inhibitor concentration causing 50% inhibition) could be estimated by fitting V = V_max / (1 + [I]/K_I) to the data by least square ([I] is the concentration of the inhibitors Fe²⁺ or Fe³⁺). The estimated K_I values are shown