Enzymatic removal of lignin from plant materials
Sidhu, Sudeep Singh
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Lignin is the major contributor to lignocellulosic recalcitrance to microbial degradation. Lignin acts as a protective matrix making cellulosic and hemicellulosic components inaccessible to microbes, hence slowing down the decomposition process. My research involved application of laccase enzyme for lignin removal from lignocellulosic biomass and its impact on two different applications. Accumulation of excessive organic matter in the form of thatch layer in turfgrass systems is a major problem and is believed to be due to slow rate of organic matter decomposition. Experiments were conducted in this study to examine the effects of laccase treatment on thatch buildup in turf. Direct application of laccase at 2.06 units cm-2 on potted creeping bentgrass in greenhouse every two weeks for nine months demonstrated a 45 and 32% reduction in thatch layer and organic matter relative to control. Field experiments on creeping bentgrass to optimize rate and frequency of laccase application showed that laccase application at rate as low as 0.5 units cm-2 applied once every two weeks or at rate 2.0 units cm-2 once every twelve weeks was effective to reduce thatch when applied for six months. An 18-22% and 21-30% reduction in thatch layer was observed with bi-weekly application of laccase at 2.0 units cm-2 for a period of six months for bermudagrass and zoysiagrass, respectively. Lignin removal from lignocellulosic biomass is an essential pretreatment step in bioethanol production to increase accessibility of structural sugars. Experiments were conducted to examine the potential of using laccase in such pretreatment to remove lignin from bioethanol feedstock materials. Sweet sorghum and switchgrass were treated with laccase mediator system consisting of ABTS (2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid), HBT (1-hydroxybenzotriazole), and violuric acid to optimize mediator concentration. A 25.5 and 24% lignin from sweet sorghum was removed at 1.88 and 1.25 mM concentration of HBT and violuric acid, respectively. In switchgrass, reduction of 28% lignin was observed at 0.63 mM concentration of violuric acid. Application of laccase has the potential to develop as a new method for thatch management. Future research is needed to determine the effectiveness of enzymatic pretreatment for improving the bioethanol production efficiency.