The Chemistry of Lignin Degradation by White-Rot Fungi

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Abstract
It has been demonstrated by Nimz et and Kirk et aLz2 that properly prepared 14C-labeled DHPs of coniferyl alcohol contain essentially the same units as those in natural lignin; therefore, the synthetic 14C-labeled lignins are suitable as a lignin model for investigations to elucidate the degradation process of lignin in nature. Crawford and Crawfordz4 and Crawford et al." studied the degradation of I4C-labeled lignins from oak, maple, and cattail tissues by various natural inocula. They demonstrated that rates of degradation varied substantially with the inoculum source. During 30 to 35 days of incubation, up to about 42% conversion to 14C02 was observed in one soil sample, and over 30% conversion of 14C02 was observed in one water sample. Hackett et al.z3 reported the lignin degradation in a variety of natural materials using synthetic I4C-lignin labeled in the side chains, aromatic ring, or methoxyl groups. They demonstrated that evolution of l4CO2 was observed when the radioactive DHP was incubated with various natural materials, such as soils, lake sediments, silage, animal bedding, and rumen contents under aerobic conditions. No release of 14C02 occurred under anaerobic conditions (see also Volume I, Chapter 5). Aerobic degradation of the radioactive DHP varied greatly with the type of materials employed. In a 78-day period, over 42% conversion to l4COZ was observed in one soil from Yellowstone National Park, although degradation to l4COZ was considerable slower in most of the samples. The results mentioned above apparently indicate that DHPs are decomposed by various microorganisms in nature. However, it is not yet clear what kinds of microorganisms in nature are responsible or which components of DHP are degraded by the microflora.

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