Inhibition of p-cresol on aerobic biodegradation of carbazole, and sodium salicylate by Pseudomonas putida

A PAH- and phenol-degrading microorganism, Pseudomonas putida (ATCC 17484), was used to study the substrate interactions during cell growth on carbazole-containing mixtures with p-cresol and sodium salicylate. Both p-cresol and sodium salicylate could be utilised by the bacteria as the sole carbon and energy sources. When cells grew on the mixture of carbazole, p-cresol and sodium salicylate, strong substrate interactions were observed. Carbazole degradation started only after p-cresol was significantly or completely removed, and the removal of carbazole was incomplete when the initial p-cresol concentration was higher than 20 mg/l. No carbazole was removed at all when the initial p-cresol concentration in the system was higher than 120 mg/l. When cells grew on the ternary substrates, the specific growth rate was found to increase with p-cresol concentration up to 50 mg/l (from 0.33 to 0.45 h−1) but decreased monotonically with higher concentrations. At 120 mg/l p-cresol, specific growth rate fell to 0.33 h−1. The inhibitory effect of p-cresol was demonstrated where carbazole degradation was immediately halted when 50 mg/l p-cresol was spiked to a system containing carbazole and sodium salicylate. Besides, the addition of p-cresol was also found to inhibit the degradation of sodium salicylate. With p-cresol, an increase in lag time was observed and the utilisation of sodium salicylate as carbon source was severely retarded.