Bibra Mohit, Kunreddy Venkat Reddy, Sani Rajesh K
Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA.
BuG ReMeDEE Consortium, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA.
Microorganisms. 2018 Sep 5;6(3):93. doi: 10.3390/microorganisms6030093.
The aim of the current study was to optimize the production of xylanase, and its application for ethanol production using the lignocellulosic biomass. A highly thermostable crude xylanase was obtained from the sp. strain DUSELR13 isolated from the deep biosphere of Homestake gold mine, Lead, SD. sp. strain DUSELR13 produced 6 U/mL of the xylanase with the beechwood xylan. The xylanase production was improved following the optimization studies, with one factor at a time approach, from 6 U/mL to 19.8 U/mL with xylan. The statistical optimization with response surface methodology further increased the production to 31 U/mL. The characterization studies revealed that the crude xylanase complex had an optimum pH of 7.0, with a broad pH range of 5.0⁻9.0, and an optimum temperature of 75 °C. The ~45 kDa xylanase protein was highly thermostable with t of 48, 38, and 13 days at 50, 60, and 70 °C, respectively. The xylanase activity increased with the addition of Cu Zn, K and Fe at 1 mM concentration, and Ca, Zn, Mg, and Na⁺ at 10 mM concentration. The comparative analysis of the crude xylanase against its commercial counterpart Novozymes Cellic HTec and Dupont, Accellerase XY, showed that it performed better at higher temperature, hydrolyzing 65.4% of the beechwood at 75 °C. The DUSEL R13 showed the mettle to hydrolyze, and utilize the pretreated, and untreated lignocellulosic biomass: prairie cord grass (PCG), and corn stover (CS) as the substrate, and gave a maximum yield of 20.5 U/mL with the untreated PCG. When grown in co-culture with , it produced 3.53 and 3.72 g/L ethanol, respectively with PCG, and CS. With these characteristics the xylanase under study could be an industrial success for the high temperature bioprocesses.
本研究的目的是优化木聚糖酶的生产及其在利用木质纤维素生物质生产乙醇中的应用。从南达科他州利德市霍姆斯特克金矿深部生物圈分离得到的 菌株DUSELR13中获得了一种高度耐热的粗木聚糖酶。 菌株DUSELR13以山毛榉木聚糖产生6 U/mL的木聚糖酶。通过一次一个因素的优化研究，木聚糖酶产量从6 U/mL提高到了以木聚糖计的19.8 U/mL。采用响应面法进行的统计优化进一步将产量提高到31 U/mL。特性研究表明，粗木聚糖酶复合物的最适pH为7.0，pH范围为5.0⁻9.0，最适温度为75℃。约45 kDa的木聚糖酶蛋白具有高度耐热性，在50℃、60℃和70℃下的半衰期分别为48天、38天和13天。在1 mM浓度下添加Cu、Zn、K和Fe以及在10 mM浓度下添加Ca、Zn、Mg和Na⁺时，木聚糖酶活性增加。将粗木聚糖酶与其商业同类产品诺维信Cellic HTec和杜邦Accellerase XY进行比较分析表明，它在较高温度下表现更好，在75℃水解65.4%的山毛榉木。DUSEL R13表现出水解和利用预处理及未处理的木质纤维素生物质（草原绳草（PCG）和玉米秸秆（CS））作为底物的能力，以未处理的PCG为底物时最大产量为20.5 U/mL。当与 共培养时，分别以PCG和CS为底物产生3.53 g/L和3.72 g/L乙醇。基于这些特性，所研究的木聚糖酶在高温生物过程中可能会取得工业成功。
