科學家對一批細菌進行了遺傳改造,，從而把纖維素轉化成乙醇,，他們提出這可能會顯著降低纖維素乙醇生產的成本。Lee Lynd及其同事改造了一種能讓木聚糖（存在于幾乎所有植物中的一種化合物）和來源于生物質的糖發(fā)酵的細菌,，從而以很高的產量生產乙醇,。這組科學家利用天然細菌培育出了他們的這種細菌，前者不但能讓纖維素和其他生物質發(fā)酵產生乙醇,，而且還能生產出有機酸,。他們制造了一個基因敲除從而消除了這些酸，剩下乙醇作為唯一可檢測到的有機產物,。
這組作者報告說這種新的嗜熱細菌ALK2可以在50攝氏度用生物質中的所有糖制造乙醇,，而傳統的發(fā)酵細菌不能在37攝氏度之上運作。他們報告說更高的工作溫度讓ALK2利用的酶比傳統細菌所需的更少,，這又可能減少工業(yè)過程的成本,。迄今達到的最高濃度是4%（按重量計算）。這組科學家預計未來的改進將讓他們達到更高的濃度,。相關論文發(fā)表在美國《國家科學院院刊》（PNAS）上,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
