where t is time (h), x(t) is the biomass as a function of time t, ms is the maintenance energy (mmol (biomass unit h)−1), Yxsm is the maximum growth yield (biomass units per mmol of a limiting substrate),
rs is the supply rate of the growth-limiting substrates in thecurrent study (mmol h−1) that was equal to 0.390 C-mmol substrate h−1 in acetate-limited retentostats and 0.495 C-mmol substrate h−1
in acetate plus benzoate-limited retentostats, and x0 is the measured biomass at time 0. Values for ms and Yxsm were taken from a previous study on the physiology of G. metallireducens in retentostats under acetate limitation in the presence of humic acid as an electron acceptor , and were −0.016 mmol (biomass unit h)−1 and 0.053 g biomass per mol substrate, respectively.