Lignocellulose is recalcitrant to enzymatic degradation due to the crystalline structure of the cellulose polymers and strong bonding to lignin, and the main components of lignocellulose include complex carbohydrate and aromatic polymers. Microbial degradation of lignocellulose is conventionally initiated by enzymes produced by lignocellulolytic fungi or bacteria.
A team of researchers led by Professor Thomas J. DiChristina from the Georgia Institute of Technology developed a microbially-driven Fenton reaction that fragments cellulose and hemicellulose, degrades cellodextrins and xylodextrins, and produces short-chain oligosaccharides and monomeric sugars in a single bioreactor. The research work is now published in Bioresource Technology.
According to the authors, the microbially-driven Fenton reaction was introduced to generate extracellular HO radicals that fragmented cellulose and hemicellulose, degraded cellodextrins and xylodextrins, and produced short-chain oligosaccharides and monomeric sugars in a single bioreactor system that operated at neutral pH conditions. Instead of the conventional lignocellulose-degrading enzymes, cellulose and xylan were fragmented and degraded by a microbially-driven Fenton reaction in a single bioreactor.
They confirmed the ability of the microbially-driven Fenton reaction to degrade carboxymethyl cellulose CMC and xylan in Fe(III)-amended liquid batch cultures exposed to nine alternating aerobic and anaerobic phases. The initial 78 h time period shows that the total number of carboxymethyl cellulose and xylan reducing ends increased sharply, indicating that shorter oligosaccharides were produced through degradation of the partially fragmented carboxymethyl cellulose and xylan polymers. The total number of xylan-reducing ends exposed during xylan fragmentation was 2-fold greater than the number of carboxymethyl cellulose reducing ends exposed during CMC fragmentation. The authors found that the rates of microbially-catalyzed Fe(III) reduction and O2-catalyzed Fe(II) oxidation were not affected by the presence of carboxymethyl cellulose or xylan.
The newly developed microbially-driven Fenton reaction reported in this study was able to produce a suite of short-chain oligosaccharides and fermentable sugars that were subsequently transformed enzymatically to the more readily degradable bioplastic polyhydroxybutyrate (PHB; published in Applied and Environmental Microbiology). Their research thus laid the foundation for development of consolidated bioprocesses for lignocellulose degradation that may be linked to downstream production of a myriad of useful bioproducts, such as ethanol, butanol, biodiesel, bioplastic, and lactic acid.
Ramanan Sekar, Hyun Dong Shin, Thomas J. DiChristina, Direct Conversion of Cellulose and Hemicellulose to Fermentable Sugars by a Microbially-Driven Fenton Reaction, Bioresource Technology 218 (2016) 1133–1139.
Sekar, R., H-D. Shin, and T. DiChristina. 2016. Activation of an otherwise silent xylose metabolic pathway in Shewanella oneidensis. Applied and Environmental Microbiology, 82:3996-4005.
School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, United States.Go To Bioresource Technology