Bioprocessing and Biofuel Research Lab, Department of Biology and Environmental Science, Auburn University at Montgomery, Montgomery, AL, USA.
Department of Agriculture, School of Agriculture and Applied Sciences, Alcorn State University, Lorman, MS, USA.
Appl Biochem Biotechnol. 2020 May;191(1):444-462. doi: 10.1007/s12010-020-03258-1. Epub 2020 Apr 4.
Lignocellulose biomass contain large macromolecules especially cellulose and hemicelluloses that can be converted to fuel and chemicals using microbial biocatalysts. This study presents comprehensive optimization of production of biomass-hydrolyzing enzymes (BHE) by a high β-glucosidase-producing Trichoderma SG2 for bioconversion of lignocellulose biomass. Overall, a mixture of paper powder and switchgrass was most suited for production of BHE in submerged fermentation (SmF). BHE production was significantly different for various organic and inorganic nitrogen sources. The combination of peptone, yeast extract, and ammonium sulfate resulted in the highest activities (Units/mL) of BHE: 9.85 ± 0.55 cellulase, 38.91 ± 0.31 xylanase, 21.19 ± 1.35 β-glucosidase, and 7.63 ± 0.31 β-xylosidase. Surfactants comparably enhanced BHE production. The highest cellulase activity (4.86 ± 0.55) was at 25 °C, whereas 35 °C supported the highest activities of xylanase, β-glucosidase, and β-xylosidase. A broad initial culture pH (4-7) supported BHE production. The T for cellulase and xylanase was 50 °C. β-xylosidase and β-glucosidase were optimally active at 40 and 70 °C, respectively; pH 5 resulted in highest cellulase, β-glucosidase, and β-xylosidase activities; and pH 6 resulted in highest xylanase activity. Response surface methodology (RSM) was used to optimize major medium ingredients. BHE activities were several orders of magnitude higher in solid-state fermentation (SSF) than in SmF. Therefore, SSF can be deployed for one-step production of complete mixture of Trichoderma SG2 BHE for bioconversion of biomass to saccharide feedstock.
木质纤维素生物质含有大量的大分子物质，特别是纤维素和半纤维素，可以使用微生物生物催化剂将其转化为燃料和化学品。本研究全面优化了高β-葡萄糖苷酶产生菌曲霉菌 SG2 生产生物质水解酶（BHE），用于生物转化木质纤维素生物质。总的来说，纸粉和柳枝稷的混合物最适合在浸没发酵（SmF）中生产 BHE。各种有机和无机氮源对 BHE 的生产有显著影响。组合使用蛋白胨、酵母提取物和硫酸铵可使 BHE 的酶活（单位/mL）达到最高：9.85±0.55 纤维素酶、38.91±0.31 木聚糖酶、21.19±1.35β-葡萄糖苷酶和 7.63±0.31β-木糖苷酶。表面活性剂同样能提高 BHE 的产量。在 25°C 时，纤维素酶的活性最高（4.86±0.55），而 35°C 时，木聚糖酶、β-葡萄糖苷酶和β-木糖苷酶的活性最高。初始培养 pH 值较宽（4-7）有利于 BHE 的生产。纤维素酶和木聚糖酶的 T 值为 50°C。β-木糖苷酶和β-葡萄糖苷酶的最适活性温度分别为 40°C 和 70°C；pH 5 时，纤维素酶、β-葡萄糖苷酶和β-木糖苷酶的活性最高；pH 6 时，木聚糖酶的活性最高。响应面法（RSM）用于优化主要培养基成分。固态发酵（SSF）中的 BHE 活性比 SmF 高几个数量级。因此，SSF 可用于一步法生产完整的曲霉菌 SG2 BHE 混合物，用于生物转化生物质为糖原料。
