Optimizing Yeast For Xylose Fermentation Through Systems Biology

随着化石燃料价格的上涨以及我们对空气质量差、温室气体排放和气候变化对健康影响的日益关注，我们越来越多地寻求可再生替代能源，如乙醇。目前，世界上大部分乙醇是由甘蔗或玉米发酵生产的。然而，纤维素发酵具有许多优点，因为纤维素是植物细胞壁的主要成分，在农业和林业废物中含量丰富，并且不与食物来源竞争。不幸的是，在使纤维素乙醇生产成为商业上可行的工业方面仍然存在许多障碍。一个问题是，我们已经使用酵母来制造酒精1000多年了，虽然在从谷物和葡萄中发现的葡萄糖等单糖中制造酒精方面非常有效，但在从木糖等复杂糖中制造酒精方面效率低下。由于纤维素的糖含量的显著百分比是木糖，因此优化酵母中的木糖发酵是必要的。传统上，为了解决这个问题，已经将来自其他物种的在木糖利用中具有已知作用的基因并入酵母中;然而木糖发酵仍然是低效的。与采取“定向”方法相比，这受到我们目前对调节木糖发酵的基因的知识水平的限制，Baetz实验室最近采取了一种全球性的方法，我们系统地筛选了酵母中的几乎每一个基因，看看去除一个基因对木糖发酵是否有负面或正面的影响。令人惊讶的是，我们发现，去除或删除四个基因，与木糖代谢没有已知的联系，显着提高酵母发酵木糖的能力。这说明了执行无偏见的全局或全基因组筛选的能力。该提案的目的是扩展我们的全基因组研究，以了解这四个基因的缺失如何导致有效的木糖发酵，并进一步表征调节酵母发酵木糖的天然能力的基因。我们的总体目标是设计这些基因，以最大限度地从木糖中生产乙醇，这将有助于加拿大的纤维素生物燃料工业。

With the rise of fossil fuel prices and our growing concerned over the health impacts of poor air quality, greenhouse gas emission and climate change, increasingly we are looking to renewable alternative energy sources such as ethanol. Presently the majority of the world's ethanol is produced by the fermentation of sugarcane or corn. However cellulosic fermentation has many advantages as cellulose, the main component of plant cell walls, is plentiful in agricultural and forestry waste and does not compete with food sources. Unfortunately, numerous hurdles remain in making cellulosic ethanol production a commercially viable industry. One problem is the yeast we have been using to make alcohol for 1000s of years, though outstandingly efficient at making alcohol from simple sugars like glucose found in grains and grapes, are inefficient at making alcohol from complex sugars such as xylose. As a significant percentage of the sugar content of cellulose is xylose, it is essential to optimize xylose fermentation in yeast. Traditionally, to address this issue genes with known roles in xylose utilization from other species have been incorporated into yeast; however xylose fermentation is still inefficient. In contrast to taking a "directed" approach, which is limited by our present state of knowledge of the genes regulating xylose fermentation, the Baetz lab has recently taken a global approach where we systematically screened nearly every gene in yeast to see if removing a gene had negative or positive impact on xylose fermentation. Surprisingly, we found that the removal or deletion of four genes, with no known connection to xylose metabolism, dramatically improved yeast's ability to ferment xylose. This illustrates the power of performing un-biased global or genome-wide screens. The aim of this proposal is to extend our genome-wide studies to understand how the deletion of these four genes results in efficient xylose fermentation and to further characterize the genes regulating yeast's natural ability to ferment xylose. Our overall goal will be to engineer these genes to maximize ethanol production from xylose, which will aid the cellulosic biofuels industry in Canada.