In acetate plus benzoate-limited retentostats, acetate (2.5 mM) and benzoate (0.7 mM) were supplied in approximately equal carbon content (5.0 and 4.9 mmol C, respectively). In contrast to batch experiments , acetate and benzoate were consumed simultaneously. Two replicates (run 1 and run 2) had residual benzoate and one replicate (run 3) had residual acetate in the outflow (Supplementary Fig. S2). The total residual C-substrate concentrations were, however, approximately the same between the replicates
(0.7–1.0 carbon mmol L−1) (Supplementary Fig. S2). The lowest growth rates estimated for acetate plus benzoate-limited retentostats were similar to the lowest growth rates estimated for acetate-limited retentostats: 0.0021–0.0025 h−1 (Fig. 1 and Sup-plementary Fig. S2).