PNAS:经过遗传改造的细菌可实现柳枝稷到乙醇的直接转换

摘要 : 美国佐治亚大学的一项研究发现，一种经过遗传改造的降解木质纤维素的细菌不仅能够把生物质纤维素转化成糖，还能把糖转化成乙醇燃料。相关文章发表于2014年6月2日的《PNAS》杂志上。

利用植物生物质进行具有成本效率的生物燃料生产的一个主要障碍是利用微生物发酵制造乙醇之前的化学和酶预处理的成本。微生物工程的工作的方向因此一直放在了制造可以执行向乙醇的生物质转化的所有阶段的一种微生物菌株上，包括把植物纤维素分解成糖并且把得到的糖发酵成乙醇。

Janet Westpheling及其同事试图改造热解纤维素菌(Caldicellulosiruptor bescii)，把糖发酵成乙醇的能力加入到这种能够把木质纤维素转换成糖的细菌中。这组作者删除了C. bescii的一个乳酸脱氢酶基因，引入了制造乙醇的热纤梭菌(Clostridium thermocellum)的一个乙醛/乙醇脱氢酶基因，因此，这种经过改造过的C. bescii菌株把柳枝稷生物质转化成了它的总发酵终产物的70%，相比之下野生型菌株的产量是0%。

这组作者说，这些结果提示，一种细菌通过执行从柳枝稷生物质原料开始的乙醇生产全阶段，可能有助于绕过昂贵的化学和酶生物质预处理。

原文摘要：

Direct conversion of plant biomass to ethanol by engineeredCaldicellulosiruptor bescii

Daehwan Chung, Minseok Cha, Adam M. Guss and Janet Westpheling

Ethanol is the most widely used renewable transportation biofuel in the United States, with the production of 13.3 billion gallons in 2012 [John UM (2013) Contribution of the Ethanol Industry to the Economy of the United States]. Despite considerable effort to produce fuels from lignocellulosic biomass, chemical pretreatment and the addition of saccharolytic enzymes before microbial bioconversion remain economic barriers to industrial deployment [Lynd LR, et al. (2008) Nat Biotechnol 26(2):169–172]. We began with the thermophilic, anaerobic, cellulolytic bacterium Caldicellulosiruptor bescii, which efficiently uses unpretreated biomass, and engineered it to produce ethanol. Here we report the direct conversion of switchgrass, a nonfood, renewable feedstock, to ethanol without conventional pretreatment of the biomass. This process was accomplished by deletion of lactate dehydrogenase and heterologous expression of a Clostridium thermocellum bifunctional acetaldehyde/alcohol dehydrogenase. Whereas wild-type C. bescii lacks the ability to make ethanol, 70% of the fermentation products in the engineered strain were ethanol [12.8 mM ethanol directly from 2% (wt/vol) switchgrass, a real-world substrate] with decreased production of acetate by 38% compared with wild-type. Direct conversion of biomass to ethanol represents a new paradigm for consolidated bioprocessing, offering the potential for carbon neutral, cost-effective, sustainable fuel production.

作者：生物帮

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