Chlorination of lignin by ubiquitous fungi has a likely role in global organochlorine production

摘要

Soils and decayed plant litter contain significant quantities of chlorinated aromatic polymers that have a natural but largely unknown origin. We used cupric oxide ligninolysis coupled with gas chromatography/mass spectrometry to show that Curvularia inaequaHs, a widely distributed litter ascomycete, chlorinated the aromatic rings of lignin in wood that it was degrading. In aspen wood decayed for 24 weeks, two chlorolignin fragments, 5-chlorovanillin and 2-chlorosyringaldehyde, were each found at ≈ 10 μg/g of wood (dry weight). These levels resemble those of similar structures generally found in unpolluted environmental samples. Fractionation of the extractable proteins followed by tandem mass spectrometric analysis showed that the colonized wood contained a previously described C. inaequalis chloroperoxi-dase that very likely catalyzed lignin chlorination. Chlorolignin produced by this route and humus derived from it are probably significant components of the global chlorine cycle because chlo-roperoxidase-producing fungi are ubiquitous in decaying lignocel-lulose and lignin is the earth's most abundant aromatic substance.