Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Department of Forensic Science and Technology, Zhejiang Police College, Hangzhou 310053, China.
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):E5308-E5316. doi: 10.1073/pnas.1703321114. Epub 2017 Jun 19.
Acetic acid can be generated through syngas fermentation, lignocellulosic biomass degradation, and organic waste anaerobic digestion. Microbial conversion of acetate into triacylglycerols for biofuel production has many advantages, including low-cost or even negative-cost feedstock and environmental benefits. The main issue stems from the dilute nature of acetate produced in such systems, which is costly to be processed on an industrial scale. To tackle this problem, we established an efficient bioprocess for converting dilute acetate into lipids, using the oleaginous yeast in a semicontinuous system. The implemented design used low-strength acetic acid in both salt and acid forms as carbon substrate and a cross-filtration module for cell recycling. Feed controls for acetic acid and nitrogen based on metabolic models and online measurement of the respiratory quotient were used. The optimized process was able to sustain high-density cell culture using acetic acid of only 3% and achieved a lipid titer, yield, and productivity of 115 g/L, 0.16 g/g, and 0.8 g⋅L⋅h, respectively. No carbon substrate was detected in the effluent stream, indicating complete utilization of acetate. These results represent a more than twofold increase in lipid production metrics compared with the current best-performing results using concentrated acetic acid as carbon feed.
醋酸可以通过合成气发酵、木质纤维素生物质降解和有机废物厌氧消化来生成。微生物将醋酸转化为三酰基甘油用于生物燃料生产具有许多优势，包括低成本甚至负成本的原料和环境效益。主要问题源于此类系统中产生的醋酸的稀释性质，这使得在工业规模上处理醋酸变得成本高昂。为了解决这个问题，我们使用产油酵母 在半连续系统中建立了一种将稀醋酸高效转化为脂类的生物工艺。所采用的设计方案使用盐和酸形式的低浓度醋酸作为碳源，并使用交叉过滤模块进行细胞回收。基于代谢模型和呼吸商的在线测量，对醋酸和氮进行了进料控制。优化后的工艺能够使用浓度仅为 3%的醋酸维持高密度细胞培养，分别实现了 115 g/L 的脂质浓度、0.16 g/g 的产率和 0.8 g⋅L⋅h 的生产力。在流出物中未检测到碳源，表明醋酸被完全利用。与使用浓醋酸作为碳源的当前表现最佳结果相比，这些结果分别代表脂质产量指标提高了两倍以上。
