Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6341, USA ; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6037, USA.
Forage Improvement Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA ; Current address: Qingdao Institute of Bioenergy and Bioprocess Technology, CAS, No.189 Songling Rd, Qingdao City, Shandong Province 266101, People's Republic of China.
Biotechnol Biofuels. 2014 May 22;7:75. doi: 10.1186/1754-6834-7-75. eCollection 2014.
Switchgrass is an abundant and dedicated bioenergy feedstock, however its inherent recalcitrance is one of the economic hurdles for producing biofuels. The downregulation of the caffeic acid O-methyl transferase (COMT) gene in the lignin pathway of switchgrass reduced lignin content and S/G ratio, and the transgenic lines showed improved fermentation yield with Saccharomyces cerevisiae and wild-type Clostridium thermocellum (ATCC 27405) in comparison to the wild-type switchgrass.
Here we examine the conversion and yield of the COMT transgenic and wild-type switchgrass lines with an engineered and evolved C. thermocellum (M1570) strain. The fermentation of the transgenic switchgrass by M1570 had superior conversion relative to the wild-type control switchgrass line with an increase in conversion of approximately 20% and ethanol being the primary product accounting for 90% of the total metabolites measured by HPLC analysis.
The engineered and evolved C. thermocellum M1570 was found to respond to the apparent reduced recalcitrance of the COMT switchgrass with no substrate inhibition, producing more ethanol on the transgenic feedstock than the wild-type substrate. Since ethanol was the main fermentation metabolite produced by an engineered and evolved C. thermocellum strain, its ethanol yield on a transgenic switchgrass substrate (gram/gram (g/g) glucan liberated) is the highest produced thus far. This result indicates that the advantages of a modified feedstock can be combined with a modified consolidated bioprocessing microorganism as anticipated.
柳枝稷是一种丰富且专用的生物能源原料，但由于其内在的抗降解性，成为生产生物燃料的经济障碍之一。木质素途径中的咖啡酸-O-甲基转移酶（COMT）基因下调降低了木质素含量和 S/G 比，与野生型柳枝稷相比，转基因株系显示出与酿酒酵母和野生型嗜热梭菌（ATCC 27405）发酵产率提高。
在这里，我们用工程化和进化的嗜热梭菌（M1570）菌株来检验 COMT 转基因和野生型柳枝稷株系的转化和产率。与野生型对照柳枝稷相比，M1570 对转基因柳枝稷的发酵具有更高的转化率，转化率增加了约 20%，而乙醇是通过 HPLC 分析测量的总代谢物的主要产物，占 90%。
发现工程化和进化的嗜热梭菌 M1570 对 COMT 柳枝稷的明显降低的抗降解性有反应，在转基因饲料上产生的乙醇比野生型底物更多。由于乙醇是工程化和进化的嗜热梭菌菌株产生的主要发酵代谢物，因此其在转基因柳枝稷底物（每克释放的葡聚糖克数）上的乙醇产率是迄今为止最高的。这一结果表明，改性饲料的优势可以与改性的综合生物加工微生物相结合，正如预期的那样。
