Depolymerisation of macromolecules from Morwell brown coal by mesophilic and thermotolerant aerobic microorganisms

Abstract

Brown coal and lignites are used as sole carbon source by a wide range of microorganisms. The majority of these are limited to utilising the tetrahydrofuran (THF) soluble portion of coal, usually equated with the mobile phase, and are unable to use the THF insoluble fraction, commonly equated with the macromolecular matrix that comprises the bulk of the coal. We report here on isolation by enrichment of microbes able to use THF insoluble Morwell brown coal as carbon source that are able to substantially reduce the apparent molecular weight of alkali solubilised THF insoluble coal. This, in conjunction with their ability to use anthraquinones and a range of diaryl compounds is consistent with their possessing novel enzymatic pathways capable of cleaving coal macromolecules. Neither lignin peroxidase nor manganese-dependent peroxidase were detected in these strains, although we have subsequently shown that Phanerochaete chrysosporium that produces these non-specific oxidase systems is able to depolymerise THF insoluble lignite quantitatively. We found that metal ions at the concentrations commonly present in microbial growth media caused an apparent increase in the molecular weight of Morwell coal and must be removed prior to estimating molecular weight changes induced by microbial activity.