Microbial Degradation of Dilignols as Lignin Models

Publisher Website
Google Scholar
Abstract
A. Present Views about the Role of Soil Microorganisms in Lignin Degradation Several papers recently appeared which surveyed the role of microorganisms in lignin degrada t i~n . ' .~ These papers indicated that white rot fungi, which are wood-destroying Basidiomycetes, are the most active and best adapted lignin degraders, while brown and soft rot fungi may degrade lignin only to some extent or are presumed only to alter it.'-l0 The ecological role of bacteria in lignin degradation is still a matter of conjecture. Some authors regard them as not very vigorous decomposers of this polymer,"-l3 while others suggest that they may degrade and even utilize lignin as a carbon source. 1 4 - 1 6 Our interest in microbial lignin degradation and transformation does not originate primarily from a wood pathology standpoint. We are interested in gaining a knowledge of the transformation of lignified plant materials in soils - especially in arable soils - and in the role of lignin in the formation of h ~ r n u s ' ~ - ' ~ (see Volume I, Chapter 4). Humus formation in soil is carried out by mixed populations of bacteria, micro-, and even macrofungi. They live together in the soil environment, where degradation and transformation of plant materials are regulated by available nutrient sources, physical ' conditions, and ~ l i m a t e . ~ ' . ~ ' In arable soil, basidiomycetes - especially white rot fungi - were only found to a limited extent. Transformation of lignified plant materials is probably conducted mainly by microfungi and b a ~ t e r i a . ~ ~ - ~ W n l y in forest soils which contain a great deal of highly lignified woody residues is there evidence for the participation of basidiomycetes in the transformation of this plant material into humus.26 Established facts and theories about the transformation of lignin into humus are exhaustively covered in Volume I , Chapter 4. However, it should be pointed out that there is no evidence that soil organic matter contains very much material which can be directly traced back to lignin.17-30 This indicates that during lignin transformation in soils this material is highly altered and degraded before it can be designated as humus. To explain these processes, it is necessary to obtain a better knowledge about the potentials of single microbes for lignin degradation and their mode of attack. To get this knowledge, we made use of a method of labeling lignins in specific carbon atoms with 14C and allowed them to be degraded by single organisms or by the mixed microbial flora of the soil. This method also makes it possible to trace back single carbons of the lignin skeleton during their transformation into humus. We were also interested in discovering to what extent microbes transform labeled phenols with structural relationship to lignin (Volume I, Chapter 4). More recently, we also became interested in waste lignins, especially in lignin sulfonates, and how they react with soil organisms or the soil itself.

This publication has 1 reference indexed in Scilit: