Canadian Journal of Chemical Engineering, Vol.87, No.3, 499-506, 2009
RELATIVE RATES AND MECHANISMS OF BIODEGRADATION OF DIESTER PLASTICIZERS MEDIATED By RHODOCOCCUS RHODOCHROUS
Di-ester plasticizers undergo slow degradation resulting in the release of recalcitrant, toxic metabolites in the environment. It is demonstrated here that the first and rate-limiting step in their co-metabolism by Rhodococcus rhodochrous is the hydrolysis of one ester bond. This mechanism is different than one proposed earlier for direct biodegradation of di-2-ethylhexyl phthalate. Also, using butyl butyrate as a reference compound to compare the relative rates of hydrolysis of different di-ester plasticizers, biodegradation rates were found to be strongly influenced by steric hindrances and solubility. Esterase activity associated with the hydrolysis of these bonds was located in the envelope of the bacterial cell. The esterase activity was not induced by specific substrates and was detected at all stages of growth. These considerations are important for the hydrolysis of recalcitrant plasticizers by a process of co-metabolism, which leads to a slow but steady overall rate of biodegradation. This suggests that as the growing reservoir of plasticizers in the environment slowly undergoes biotransformation, recalcitrant toxic metabolites will be continuously released.