Biodegradation of seven phthalate esters by Bacillus mojavensis B1811

Phthalate esters (PAEs) are one of the most widely used groups of plasticizers and have been considered threats to the environment and human health. This study investigated the efficient biodegradation of seven phthalate esters (PAEs) by Bacillus mojavensis B1811. The results showed that di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), benzyl butyl phthalate (BBP) and dipentyl phthalate (DPP) could be almost completely degraded by strain B1811 within four days in mineral salt medium (MSM) under shaking conditions, while only 5.9% of the dimethyl phthalate (DMP) and 42.9% of the diethyl phthalate (DEP) present, which both have short alkyl chains, were degraded by strain B1811 under the same conditions. An esterase activity assay also indicated that the specific activities of esterases induced by PAEs with longer alkyl chains were much higher than those of esterases induced by PAEs with short alkyl chains. High-performance liquid chromatography-electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) was applied to identify the major metabolites of the seven PAEs. The PAEs were first degraded to the corresponding phthalate monoesters and then degraded to phthalic acid; phthalic acid was rapidly degraded to produce benzoic acid which was subsequently converted to protocatechuate and ultimately transformed to CO2 and H2O. The optimal conditions for biodegradation were also obtained and an exponential model was the best model to represent the PAEs depletion. It is therefore concluded that B. mojavensis B1811 offers great application potential in the bioremediation of environments polluted with PAEs.