Response of Pseudomonas putida F1 cultures to fluctuating toluene loads and operational failures in suspended growth bioreactors.

The response of Pseudomonas putida F1 to process fluctuations and operational failures during toluene biodegradation was evaluated in a chemostat suspended growth bioreactor. The ability of P. putida F1 to rapidly increase its specific toluene degradation capacity resulted in no significant variation in process removal efficiency when toluene load was increased from 188 to 341 g m(-3) h(-1). Likewise, bacterial activity rapidly reached steady state performance (in less than 1.5 h after the restoration of steady state operational conditions) following an 8 h process shutdown, or after episodes of toluene or mineral nutrients deprivation. Process performance was however highly sensitive to pH, as pH levels below 4.5 dramatically inhibited bacterial activity, decreasing severely process robustness and inducing a cycle of periodic process collapses and recoveries. This pH mediated deterioration of bacterial activity was confirmed by further respirometric tests, which revealed a 50-60% reduction in the O(2) consumption rate during the degradation of both toluene and 3-methyl catechol when pH decreased from 5.05 to 4.55. Finally, process robustness was quantified according to methods previously described in literature.