Oxidative dehalogenation of chlorinated hydroxybiphenyls by laccases of white-rot fungi

Chlorinated biphenyls have been widely used in industry because of their advantageous chemical and physical properties. But the transformation products of chlorinated biphenyls derived from hydroxylation, the chlorinated hydroxybiphenyls, have oestrogenic, immunosuppressive, and carcinogenic activities. Because of the risks to humans and animals, the ability to transform chlorinated hydroxybiphenyls is a major goal of environmental research. We here investigated transformations of the chlorinated hydroxybiphenyls 5-chloro-2-hydroxybiphenyl, 3,5-dichloro-2-hydroxybiphenyl, and 2′,5,5′-trichloro-2-hydroxybiphenyl by laccases from Pycnoporus cinnabarinus and Myceliophthora thermophila, because very little is known about the transformation pathways of the named substances by filamentous fungi though these organisms play important roles in soil ecosystems and in contaminated sludges and wastewater. Oxidative dechlorination and formation of quinoid and hydroquinoid derivatives were observed in all three cases. Furthermore, dimer formation was detected. Therefore, laccase leads not only to dechlorination of the initial chlorinated hydroxybiphenyls but also to dechlorinated di- and oligomeric products. In addition 4-chloro-2-hydroxydibenzofuran was found and purified as a product of the laccase reaction on 3,5-dichloro-2-hydroxybiphenyl.