Bioengineering approaches to high-solids cellulose fermentation for biofuel production

这项研究的长期目标是开发一种半连续的间歇发酵工艺，使用高浓度（10%或更高）的纤维素作为生物燃料（乙醇和氢）生产的底物。我们的模式生物，Clostridium thermocellum，是一种革兰氏阳性、嗜热、产醋的厌氧菌，它可以利用纤维素作为唯一的碳源，通过混合发酵代谢合成乙醇、醋酸酯和其他有机酸，同时释放氢（H2）和二氧化碳（CO2）。本研究将着重于高固含量发酵工艺的开发。从纤维素发酵生产生物燃料提出了许多独特的生物和工程挑战，例如：i)如何将高浓度的不溶性底物移动到生物反应器中，并在生物反应器中混合底物；Ii)如何量化底物从葡萄糖长聚合物到低纤维素糊精和/或可溶性糖（纤维素二糖和葡萄糖）的转化；Iii)如何量化细胞在不溶性底物上的生长；Iv)如何回收发酵反应气相产生的乙醇；v)如何净化、捕获和储存产生的氢。这项NSERC发现基金的目标是建立在我们已经取得的进展和解决这些挑战的基础上。本提案的短期目标是：1)开发一种可靠和准确的方法来量化纤维素发酵过程中的底物转化率；2)在不溶性底物上定量细胞生长；3)整合并验证纤维素发酵过程中代谢物的连续实时监测系统。这项研究弥合了科学和工程之间的差距，开发了一种利用纤维素作为发酵底物的生物燃料生产的综合生物处理方法。纤维素底物的综合生物加工通过降低上游加工成本，为下一代生物燃料生产提供了巨大的潜力。

The long-term objective of the research is to develop a semi-continuous, fed-batch fermentation process using high concentrations (10% or greater) of cellulose as the substrate for biofuels (ethanol and hydrogen) production. Our model organism, Clostridium thermocellum, is a gram-positive, thermophilic, acetogenic, anaerobe that can utilize cellulose as a sole carbon source and synthesizes ethanol, acetate, and other organic acids via a mixed fermentation metabolism, with the concomitant release of hydrogen (H2) and carbon dioxide (CO2). This research will focus on development of the high solids fermentation process. Biofuel production from cellulose fermentation presents a number of unique biological and engineering challenges, such as: i) how to move insoluble substrate at high concentration into, and mix the substrate within, a bioreactor; ii) how to quantify conversion of the substrate from long polymers of glucose to oligocellulodextrins and/or soluble sugars (cellobiose and glucose); iii) how to quantify cell growth on an insoluble substrate; iv) how to recover the ethanol produced from the vapour phase of the fermentation reaction; and v) how to purify, capture, and store the hydrogen produced. The goal of this proposed NSERC Discovery grant is to build upon the progress that we have made and address these challenges. The short-term objectives of this proposal are to: 1) develop a reliable and accurate method to quantify rates of substrate conversion during cellulose fermentation; 2) quantify cell growth on an insoluble substrate; and 3) integrate and validate a continuous, real-time monitoring system for metabolites during cellulose fermentation. This research bridges the gap between science and engineering to develop a Consolidated Bioprocessing approach for biofuel production using cellulose as a substrate for fermentation. Consolidated Bioprocessing of cellulosic substrates offers significant potential as a viable process for next generation biofuel production by reducing upstream processing costs.