Comparison of the degradation of 14C-labeled DHP and corn stalk lignins by micro- and macrofungi and bacteria

To what extent and by which mode microfungi and bacteria from soil are able to degrade lignin have been investigated and their activity compared with those of white and brown rot Basidiomycetes. The experiments were made by means of specifically 14C-labeled DHPs prepared by polymerization of correspondingly labeled coniferyl alcohol. Also, a corn stalk material was used which was specifically labeled in the lignin part. This material was prepared by infusion of specifically labeled cinnamic acid compounds into growing maize plants. The potential of the organisms to degrade several specifically labeled phenols was determined and compared. White and brown rot fungi, as well as several microscopic fungi, were able to degrade phenolcarboxylic and cinnamic acids and even some phenolic compounds with completely alkylated phenolic hydroxl groups. They could also introduce hydroxl groups into benzoic and pi-hydroxybenzoic acids before ring cleavage. As compared to brown rot, the white rot fungi released higher amounts of CO2 from the aromatic and side chain carbons of DHP and plant lignins. Some brown rot fungi, however, had similar capacities in degrading DHP lignin as white rot fungi. They especially released more CO2 from methoxyl groups. This release was dependent upon the added carbohydrate source and could be either repressed or enhanced. Several bacteria, especially Nocardia spp. and Pseudomonas spp., were tested for their potential to degrade the labeled lignins or phenols. Most of these bacteria did not appreciably degrade lignins, although they were highly active in the metabolization of phenols. Some Nocardia spp., however, were found to have a noteworthy capacity in the degradation of lignins and phenols. Preliminary studies of the potentials of the organisms to attack labeled lignin sulfonates either in liquid or soil cultures are presented. (Refs. 100)