Joint BioEnergy Institute (JBEI), Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America.
PLoS One. 2012;7(5):e37010. doi: 10.1371/journal.pone.0037010. Epub 2012 May 23.
Generation of biofuels from sugars in lignocellulosic biomass is a promising alternative to liquid fossil fuels, but efficient and inexpensive bioprocessing configurations must be developed to make this technology commercially viable. One of the major barriers to commercialization is the recalcitrance of plant cell wall polysaccharides to enzymatic hydrolysis. Biomass pretreatment with ionic liquids (ILs) enables efficient saccharification of biomass, but residual ILs inhibit both saccharification and microbial fuel production, requiring extensive washing after IL pretreatment. Pretreatment itself can also produce biomass-derived inhibitory compounds that reduce microbial fuel production. Therefore, there are multiple points in the process from biomass to biofuel production that must be interrogated and optimized to maximize fuel production. Here, we report the development of an IL-tolerant cellulase cocktail by combining thermophilic bacterial glycoside hydrolases produced by a mixed consortia with recombinant glycoside hydrolases. This enzymatic cocktail saccharifies IL-pretreated biomass at higher temperatures and in the presence of much higher IL concentrations than commercial fungal cocktails. Sugars obtained from saccharification of IL-pretreated switchgrass using this cocktail can be converted into biodiesel (fatty acid ethyl-esters or FAEEs) by a metabolically engineered strain of E. coli. During these studies, we found that this biodiesel-producing E. coli strain was sensitive to ILs and inhibitors released by saccharification. This cocktail will enable the development of novel biomass to biofuel bioprocessing configurations that may overcome some of the barriers to production of inexpensive cellulosic biofuels.
从木质纤维素生物质中的糖生产生物燃料是替代液态化石燃料的一种很有前途的方法，但必须开发高效且廉价的生物加工配置，以使这项技术具有商业可行性。商业化的主要障碍之一是植物细胞壁多糖对酶水解的顽固性。使用离子液体 (IL) 对生物质进行预处理可以实现生物质的有效糖化，但残留的 IL 会抑制糖化和微生物燃料电池的生产，因此需要在 IL 预处理后进行广泛的清洗。预处理本身也会产生生物质衍生的抑制化合物，从而降低微生物燃料电池的生产。因此，从生物质到生物燃料生产的过程中有多个环节必须进行检查和优化，以最大限度地提高燃料产量。在这里，我们报告了通过将嗜热细菌糖苷水解酶与重组糖苷水解酶混合的混合群落产生的耐离子液体的纤维素酶混合物的开发。与商业真菌混合物相比，这种酶混合物可以在更高的温度和更高的 IL 浓度下糖化 IL 预处理的生物质。使用这种混合物从 IL 预处理的柳枝稷中获得的糖可以通过代谢工程大肠杆菌菌株转化为生物柴油（脂肪酸乙酯或 FAEEs）。在这些研究中，我们发现这种生产生物柴油的大肠杆菌菌株对 IL 和糖化释放的抑制剂敏感。这种混合物将能够开发出新型的生物质到生物燃料生物加工配置，这可能克服生产廉价纤维素生物燃料的一些障碍。
