Characterization of Zalaria obscura Y1223 hydrolases: implications for lignocellulose conversion.

Abstract

Overconsumption of fossil fuel reserves and its adverse effects has sparked interest in the production of second-generation biofuels due to the abundance of lignocellulosic waste and potential energy crops. However, processing costs associated with depolymerization of the cellulose crystalline structure have stalled advancement in cellulosic ethanol production. Current investigations range from identification of novel enzymes for lignocellulose hydrolysis to consolidation of enzyme production into a singular alcohol producing microorganism to potentially reduce cost for commercial processing. In this study, a total of 828 non-Saccharomyces and black yeasts were screened for cellulolytic and xylanolytic enzyme activities, whereby 60 isolates were identified that exhibited activity for at least one of the enzymes tested. In doing so, a novel Zalaria obscura strain (Z. obscura Y1223) was identified and assessed for enzyme activity in multiple growth media. Semi-quantitative assays showed that Z. obscura Y1223 produced cellulases optimally in media containing yeast extract, peptone and oat bran, with a pH range between pH 5 and 6 and at 30 °C. Maximum xylanase activity (20.5 U/L/OD₆₀₀) was attained using synthetic complete media supplemented with xylo-oligosaccharides and maximum cellulase activity (7.51 U/L/OD₆₀₀ endoglucanase, 1.302 U/L/OD₆₀₀ β-glucosidase) was attained when grown in media containing yeast extract, peptone and oat bran. To our knowledge, this is the first study to quantify the cellulolytic and xylanolytic enzyme activities of a Zalaria spp., which provides key insight into the availability of unexplored cellulolytic enzymes that could inform the design of organisms engineered for consolidated bioprocessing.