科学家对一批细菌进行了遗传改造,从而把纤维素转化成乙醇,他们提出这可能会显著降低纤维素乙醇生产的成本。Lee Lynd及其同事改造了一种能让木聚糖(存在于几乎所有植物中的一种化合物)和来源于生物质的糖发酵的细菌,从而以很高的产量生产乙醇。这组科学家利用天然细菌培育出了他们的这种细菌,前者不但能让纤维素和其他生物质发酵产生乙醇,而且还能生产出有机酸。他们制造了一个基因敲除从而消除了这些酸,剩下乙醇作为唯一可检测到的有机产物。
这组作者报告说这种新的嗜热细菌ALK2可以在50摄氏度用生物质中的所有糖制造乙醇,而传统的发酵细菌不能在37摄氏度之上运作。他们报告说更高的工作温度让ALK2利用的酶比传统细菌所需的更少,这又可能减少工业过程的成本。迄今达到的最高浓度是4%(按重量计算)。这组科学家预计未来的改进将让他们达到更高的浓度。相关论文发表在美国《国家科学院院刊》(PNAS)上。(生物谷Bioon.com)
生物谷推荐原始出处:
PNAS,doi: 10.1073/pnas.0801266105,A. Joe Shaw,Lee R. Lynd
Metabolic engineering of a thermophilic bacterium to produce ethanol at high yield
A. Joe Shaw*,?, Kara K. Podkaminer*, Sunil G. Desai*, John S. Bardsley?, Stephen R. Rogers*, Philip G. Thorne?, David A. Hogsett?, and Lee R. Lynd*
We report engineering Thermoanaerobacterium saccharolyticum, a thermophilic anaerobic bacterium that ferments xylan and biomass-derived sugars, to produce ethanol at high yield. Knockout of genes involved in organic acid formation (acetate kinase, phosphate acetyltransferase, and L-lactate dehydrogenase) resulted in a strain able to produce ethanol as the only detectable organic product and substantial changes in electron flow relative to the wild type. Ethanol formation in the engineered strain (ALK2) utilizes pyruvate:ferredoxin oxidoreductase with electrons transferred from ferredoxin to NAD(P), a pathway different from that in previously described microbes with a homoethanol fermentation. The homoethanologenic phenotype was stable for >150 generations in continuous culture. The growth rate of strain ALK2 was similar to the wild-type strain, with a reduction in cell yield proportional to the decreased ATP availability resulting from acetate kinase inactivation. Glucose and xylose are co-utilized and utilization of mannose and arabinose commences before glucose and xylose are exhausted. Using strain ALK2 in simultaneous hydrolysis and fermentation experiments at 50°C allows a 2.5-fold reduction in cellulase loading compared with using Saccharomyces cerevisiae at 37°C. The maximum ethanol titer produced by strain ALK2, 37 g/liter, is the highest reported thus far for a thermophilic anaerobe, although further improvements are desired and likely possible. Our results extend the frontier of metabolic engineering in thermophilic hosts, have the potential to significantly lower the cost of cellulosic ethanol production, and support the feasibility of further cost reductions through engineering a diversity of host organisms.