Department of Chemical Engineering, Waterloo, Ontario, Canada.
Department of Chemical Engineering, Waterloo, Ontario, Canada.
Biotechnol Adv. 2019 Jul-Aug;37(4):538-568. doi: 10.1016/j.biotechadv.2018.10.006. Epub 2018 Oct 17.
While the widespread reliance on fossil fuels is driven by their low cost and relative abundance, this fossil-based economy has been deemed unsustainable and, therefore, the adoption of sustainable and environmentally compatible energy sources is on the horizon. Biorefinery is an emerging approach that integrates metabolic engineering, synthetic biology, and systems biology principles for the development of whole-cell catalytic platforms for biomanufacturing. Due to the high degree of reduction and low cost, glycerol, either refined or crude, has been recognized as an ideal feedstock for the production of value-added biologicals, though microbial dissimilation of glycerol sometimes can be difficult particularly under anaerobic conditions. While strain development for glycerol biorefinery is widely reported in the literature, few, if any, commercialized bioprocesses have been developed as a result, such that engineering of glycerol metabolism in microbial hosts remains an untapped opportunity in biomanufacturing. Here we review the recent progress made in engineering microbial hosts for the production of biofuels, diols, organic acids, biopolymers, and specialty chemicals from glycerol. We begin with a broad outline of the major pathways for fermentative and respiratory glycerol dissimilation and key end metabolites, and then focus our analysis on four key genera of bacteria known to naturally dissimilate glycerol, i.e. Klebsiella, Citrobacter, Clostridium, and Lactobacillus, in addition to Escherichia coli, and systematically review the progress made toward engineering these microorganisms for glycerol biorefinery. We also identify the major biotechnological and bioprocessing advantages and disadvantages of each genus, and bottlenecks limiting the production of target metabolites from glycerol in engineered strains. Our analysis culminates in the development of potential strategies to overcome the current technical limitations identified for commonly employed strains, with an outlook on the suitability of different hosts for the production of key metabolites and avenues for their future development into biomanufacturing platforms.
虽然广泛依赖化石燃料是因为它们的低成本和相对丰富，但这种基于化石的经济被认为是不可持续的，因此，采用可持续和环境兼容的能源势在必行。生物炼制是一种新兴的方法，它集成了代谢工程、合成生物学和系统生物学原理，用于开发用于生物制造的全细胞催化平台。由于还原程度高且成本低，甘油（无论是精制的还是粗制的）已被认为是生产高附加值生物制品的理想原料，尽管微生物对甘油的异化作用有时可能很困难，特别是在厌氧条件下。虽然在文献中广泛报道了用于甘油生物炼制的菌株开发，但几乎没有商业化的生物工艺因此得到开发，因此，在微生物宿主中工程化甘油代谢仍然是生物制造中的一个未开发的机会。在这里，我们综述了最近在工程微生物宿主中生产生物燃料、二醇、有机酸、生物聚合物和特种化学品方面的进展。我们首先概述了发酵和呼吸甘油异化的主要途径和关键末端代谢物，然后将我们的分析重点放在已知天然异化甘油的四个关键细菌属上，即克雷伯氏菌、柠檬酸杆菌、梭菌和乳杆菌，以及大肠杆菌，并系统地综述了为甘油生物炼制工程化这些微生物所取得的进展。我们还确定了每个属的主要生物技术和生物加工优势和劣势，以及限制目标代谢物在工程菌株中从甘油生产的瓶颈。我们的分析最终制定了潜在的策略，以克服目前为常用菌株确定的技术限制，展望不同宿主在生产关键代谢物方面的适用性及其未来发展为生物制造平台的途径。
