Abstract

Xylophagous termites are capable of degrading lignocellulose by symbiotic gut microorganisms along with the host’s indigenous enzymes. Therefore, the termite gut might be a potential niche to obtain natural yeasts with celluloytic, xylanolytic and ethanologenic traits required for bioethanol production from lignocellulosic biomass. In this study, we cultured 79 yeasts from three different termites viz. Coptotermes heimi, Odontotermes javanicus and Odontotermes obesus. After suitable screening methods, we identified 53 yeasts, which belonged to 10 genera and 16 different species of both ascomycetous and basidiomycetous yeasts. Most yeasts in the present study represent their first-ever isolation from the termite gut. Representative strains of identified yeasts were evaluated for their cellulolytic, xylanolytic, and ethanologenic abilities. None of the isolates showed cellulase activity; 22 showed xylanolytic activity, while six produced substantial quantities of ethanol. Among xylanolytic cultures, Pseudozyma hubeiensis STAG 1.7 and Hannaella pagnoccae STAG 1.14 produced 1.31 and 1.17 IU of xylanase. Among ethanologenic yeasts, the strains belonging to genera Candida and Kodamaea produced high amount of ethanol. Overall, highest ethanol level of 4.42 g/L was produced by Candida tropicalis TS32 using 1% glucose, which increased up to 22.92 g/L at 35 °C, pH 4.5 with 5% glucose. Fermentation of rice straw hydrolysate gave 8.95 g/l of ethanol with a yield of 0.42 g/g using the strain TS32. Our study highlights the gut of wood-feeding termites as a potential source of diverse yeasts that would be useful in the production of xylanase and bioethanol.

摘要

木糖蚁能够通过共生肠道微生物与宿主的固有酶一起降解木质纤维素。因此，白蚁肠道可能是获得具有木质纤维素生物质生产生物乙醇所需的纤维素，木糖酵解和产乙醇特性的天然酵母的潜在市场。在这项研究中，我们培养了来自三种不同白蚁的79种酵母。黑米乳白蚁，黑翅爪哇和黑翅金枪鱼。经过适当的筛选方法，我们鉴定了53个酵母菌，它们分别属于10属和16种不同的子囊酵母和担子菌酵母。本研究中的大多数酵母菌代表了它们从白蚁肠道中的首次分离。评价代表性酵母菌株的纤维素分解，木聚糖分解和产乙醇能力。没有分离物显示纤维素酶活性。22显示出木聚糖分解活性，而六种产生大量乙醇。在木聚糖分解培养物中，湖北假单胞菌STAG 1.7和汉纳氏菌STAG 1.14产生了1.31和1.17 IU的木聚糖酶。在产乙醇的酵母中，属于假丝酵母和科达美亚属的菌株产生了大量的乙醇。总体而言，热带假丝酵母TS32使用1％的葡萄糖生产的最高乙醇水平为4.42 g / L ，在35°C，pH 4.5和5％的葡萄糖条件下，乙醇含量最高可达22.92 g / L。用菌株TS32发酵稻草水解产物得到8.95g / l乙醇，产率为0.42g / g。我们的研究强调了以木材为食的白蚁的肠道是多种酵母的潜在来源，可用于生产木聚糖酶和生物乙醇。