Adsorption capacity as a key parameter for enzyme induction and pentachlorophenol degradation in Mycobacterium chlorophenolicum PCP-1.

Abstract

Adsorption of pentachlorophenol (PCP) on induced cells of Mycobacterium chlorophenolicum PCP-1 and its influence on enzyme induction and PCP degradation of this strain were studied. Compared to non-induced cells, induced degrading cells had a lower adsorption capacity (q(ads)), particularly at prolonged induction and low PCP concentration. Unlike the effects of pH and biomass concentration previously reported for non-induced cells, the variation of q(ads) of induced cells was associated with changes of both the capacity and intensity constants of the Freundlich equation which was used to describe PCP adsorption on M. chlorophenolicum PCP-1. This indicated changes of cell surface properties during enzyme induction and PCP degradation. The latter was shown in turn to be affected by several parameters such as PCP concentration, pH value and induction time. Interestingly, irrespective of the pH and PCP concentration, the specific PCP degradation rate (q(t)(PCP)) at a given induction time was found to be solely a function of q(ads), revealing that adsorption capacity is an inherent key parameter for enzyme induction and PCP degradation. Based on this knowledge, a kinetic model was developed for q(t)(PCP) which used only q(ads) and induction time as variables. The model considered inhibition of PCP on both enzyme induction and enzyme activity and described the experimental data at different PCP concentrations and pH values well. q(ads) also turned out to be a useful criterion for choosing optimum induction concentration of PCP. Irrespective of pH and biomass concentration, an initial adsorption capacity of 2-3 micromol PCP/g cells was found to be optimum for enzyme induction in M. chlorophenolicum PCP-1.