Inhibitory effects of catechol accumulation on benzene biodegradation in Pseudomonas putida F1 cultures

The influence of benzene concentration on the specific growth rate (μ), CO2 and metabolite production, and cellular energetic content (i.e., ATP content), during benzene biodegradation by Pseudomonas putida F1 was investigated. Within the concentration range tested (5–130 mg benzene l−1) the μ, the specific CO2 production, and the ATP content remained constant at 0.42–0.48 h−1, 1.86 ± 0.21 g CO2 g−1 biomass, and 5.3 ± 0.4 × 10−6 mol ATP g−1 biomass, respectively. Catechol accumulated during process start-up at all tested concentrations. Catechol specific production increased with increasing benzene inlet concentrations. This confirms that the transformation of this intermediate was the limiting step during benzene degradation. It was shown that catechol inhibited both the conversion of benzene to catechol and its further transformation. In addition, catechol concentrations higher than 10 mg l−1 significantly decreased both benzene and catechol associated respiration, confirming the highly inhibitory effect of this intermediate. This inhibitory threshold concentration was approximately two orders of magnitude lower than the concentrations present in the culture medium during process start-up, suggesting that cellular activity was always far below its maximum. Thus, due to its toxic and inhibitory nature and its tendency to accumulate at high benzene loading, catechol must be carefully monitored during process operation.