Improving the Cost of Producing Lignocellulosic Bioethanol: Screening Soil Microbes for Secreted Cellulolytic and Xylanolytic Activity

Abstract

Fuel ethanol is already produced in the United States from corn and other grains rich in starch. A new generation of biofuels, made from lignocellulosic biomass such as wood, grass and agricultural waste, is currently being developed as an alternative transportation fuel to gasoline. The cost of the industrial techniques used to make lignocellulosic biofuel currently prohibits its production. Part of the problem stems from the recalcitrant nature of lignocellulose, a main component of the plant cell wall and a material that is highly resistant to breakdown from the microbial and mechanical forces needed to access its fermentable sugars. The current method of production begins with a pretreatment step designed to open up lignocellulose, making its sugars more exposed to enzymatic attack. The next step is the enzymatic hydrolysis of cellulose and other polymeric sugars. Fermentation of these sugars into ethanol is the last step. To lower production cost, one method currently being experimented with is identification of microorganisms capable of combining the hydrolysis and fermentation steps into one step. This study, however, aims to find microorganisms capable of releasing fermentable sugars by combining the pretreatment and hydrolysis steps. This was done by isolating microbes that grow in media with lignocellulosic material as the only carbon source. These microbes were then analyzed for secreted cellulolytic and xylanolytic activity. Glucose and pentose assays revealed that all samples, with the exception of T26, were able to utilize short oligosaccharide glucose and xylose chains for energy, while samples C10, J7, S27 and T30 were capable of breaking down commercial xylan. Based on these results we’ve concluded that the soil microbes isolated for this study are capable of breaking down lignocellulose and hydrolyzing the cellulose and xylan within.