Selective production of low molecular weight aromatics from biomass by fungal and bacterial co-cultures

The microbial degradation of lignocellulosic biomass by lignolytic basidiomycetous fungi (Coriolus versicolor and Trametes gallica) and cellulolytic actinobacteria (Microbacterium sp. and Streptomyces sp.) was investigated. Several process parameters such as temperature, time, pH, particle size, and stirring mode were examined. Microbial treatment for 8 weeks resulted in a 5-fold reduction of particle size and up to 34 wt% biodegradation of biomass. Maximum degradation was attained by a co-culture of all four strains that removed 7 wt% of lignin and 27 wt% of polysaccharides. The yield of glucose released by cellulose hydrolysis peaked at 38 wt% on day 6 of incubation, and gradually declined thereafter. Once the sugars were depleted, production of lignolytic enzymes (laccase, manganese-dependent peroxidase, and lignin peroxidase), essential for lignin degradation, was induced. The main products of lignin biodegradation were shown to be water-soluble, low molecular weight (LMW) phenolics, and included veratryl alcohol, dehydromevalonic lactone and acetovanillone, as determined by Pyrolysis-GC-MS analysis. Treatment with white-rot fungi in absence of actinobacteria effected maximum production of lignin derivatives of lower and higher molecular weight at a ratio of 2.5 to 1, respectively. The former remained in solution whereas the latter precipitated upon acidification. As the release and uptake of the bulk of monosaccharides occurs prior to the onset of lignin biodegradation, this approach provides the opportunity to selectively fractionate and obtain LMW aromatics. The aromatic LMW products obtained from microbial degradation of lignin can serve as a renewable feedstock substitute of fossil-based petrochemicals in the synthesis of high-value green polymers.