Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 3629 Engineering Hall, 1415 Engineering Dr, Madison, WI 53706, USA.
Appl Microbiol Biotechnol. 2013 Jun;97(11):5149-59. doi: 10.1007/s00253-013-4911-0. Epub 2013 Apr 26.
Microbially synthesized fatty acids are an attractive platform for producing renewable alternatives to petrochemically derived transportation fuels and oleochemicals. Free fatty acids (FFA) are a direct precursor to many high-value compounds that can be made via biochemical and ex vivo catalytic pathways. To be competitive with current petrochemicals, flux through these pathways must be optimized to approach theoretical yields. Using a plasmid-free, FFA-producing strain of Escherichia coli, a set of chemostat experiments were conducted to gather data for FFA production under phosphate limitation. A prior study focused on carbon-limited conditions strongly implicated non-carbon limitations as a preferred media formulation for maximizing FFA yield. Here, additional data were collected to expand an established kinetic model of FFA production and identify targets for further metabolic engineering. The updated model was able to successfully predict the strain's behavior and FFA production in a batch culture. The highest yield observed under phosphate-limiting conditions (0.1 g FFA/g glucose) was obtained at a dilution rate of 0.1 h(-1), and the highest biomass-specific productivity (0.068 g FFA/gDCW/h) was observed at a dilution rate of 0.25 h(-1). Phosphate limitation increased yield (∼45 %) and biomass-specific productivity (∼300 %) relative to carbon-limited cultivations using the same strain. FFA production under phosphate limitation also led to a cellular maintenance energy ∼400 % higher (0.28 g/gDCW/h) than that seen under carbon limitation.
微生物合成脂肪酸是生产可再生替代石油化工衍生运输燃料和油脂化学品的有吸引力的平台。游离脂肪酸（FFA）是许多高价值化合物的直接前体，可以通过生化和体外催化途径来制造。为了与当前的石油化工产品竞争，必须优化这些途径的通量以接近理论产率。使用无质粒、产生 FFA 的大肠杆菌菌株，进行了一组恒化器实验，以收集在磷酸盐限制下生产 FFA 的数据。先前的研究集中在碳限制条件下，强烈暗示非碳限制是最大化 FFA 产量的首选培养基配方。在这里，收集了更多的数据来扩展 FFA 生产的现有动力学模型，并确定进一步代谢工程的目标。更新后的模型能够成功预测分批培养中菌株的行为和 FFA 生产。在磷酸盐限制条件下观察到的最高产率（0.1 g FFA/g 葡萄糖）是在稀释率为 0.1 h(-1) 时获得的，而最高的生物质特异性生产率（0.068 g FFA/gDCW/h）是在稀释率为 0.25 h(-1) 时观察到的。与使用相同菌株的碳限制培养相比，磷酸盐限制增加了产率（约 45%）和生物质特异性生产率（约 300%）。与碳限制相比，磷酸盐限制下的 FFA 生产还导致细胞维持能量增加约 400%（0.28 g/gDCW/h）。
