The biogeochemical chlorine cycle in forest ecosystems

Abstract

Organochlorine compounds, once thought to be solely anthropogenic, are now known to be produced naturally in forest ecosystems. One natural chlorination mechanism involves catalysis by the enzyme chloroperoxidase (CPO). Using hydrogen peroxide to oxidize inorganic chloride, CPO generates reactive chlorine intermediates (HOCl) capable of chlorinating non‐specific organic substrates. These reactive chlorine species are believed to be implicated in lignin degradation during plant matter decay, with organochlorine produced as a by‐product. However, certain lignin‐degrading microorganisms, including the fungus Phanerochaete chrysosporium, are known to dechlorinate anthropogenic organochlorine pollutants. To explore this paradox regarding the role of chlorine in lignin degradation, we investigated the function of different microorganisms in the biogeochemical chlorine cycle using synchrotron‐based Cl 1s X‐ray absorption near‐edge structure (XANES) spectroscopy. These tests provide evidence of chlorination through a CPO‐like mechanism by an enzyme extract of the lichen Parmotrema hypotropum and preliminary evidence of dechlorination by the fungus P. chrysosporium.Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE‐AC02–98CH10886.