Department of Biosystems Engineering, University of Manitoba, E2-376 Engineering and Information Technology Complex (EITC), 75A Chancellor's Circle, Winnipeg, MB, R3T 5V6, Canada.
Department of Microbiology, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
World J Microbiol Biotechnol. 2018 Jul 3;34(8):106. doi: 10.1007/s11274-018-2488-6.
Polyhydroxyalkanoates (PHAs) are a diverse class of bio-polymers synthesized by bacteria, usually during imbalanced growth conditions. Optimizing PHA productivity is highly dependent on the bioreactor oxygen transfer rate (OTR), which is an important consideration for process performance and economics, particularly with increasing scale. Relatively few in-depth studies are available regarding the effect of OTR and dissolved oxygen content (DOC) on PHA formation, synthesis rates, composition, and characteristics. This review examines past research studies on the effect of low DOC environments on production of short-chain length (scl-) PHAs, synthesized by both pure and mixed cultures, in order to identify opportunities and gaps concerning the effect of DOC on production of medium-chain length (mcl-) PHAs, an area that has not been studied in detail. The literature indicates that production of scl-PHA (a reductive process) acts as an electron sink allowing cells to maintain balanced redox state at low DOC. Conversely, production of mcl-PHA via fatty acid de novo synthesis (also a reductive process) does not occur to any significant extent in low DOC environments, while mcl-PHA synthesis from fatty acids (an oxidative process) can be promoted in low DOC environments. The monomer composition, molecular mass, as well as physical and thermal properties of the polymer can change in response to OTR, but further research in this area is required for both scl- and mcl-PHAs. Process design and management of bioreactor OTR in PHA production might therefore be directed by the final application of the polymer rather than cost considerations.
聚羟基脂肪酸酯（PHA）是一类由细菌合成的生物聚合物，通常在生长失衡的条件下合成。优化 PHA 的生产力高度依赖于生物反应器的氧传递速率（OTR），这是工艺性能和经济性的重要考虑因素，特别是在规模不断扩大的情况下。关于 OTR 和溶解氧含量（DOC）对 PHA 形成、合成速率、组成和特性的影响，相对较少有深入的研究。本综述考察了过去关于低 DOC 环境对短链长（scl-）PHA 生产的影响的研究，这些 PHA 由纯培养物和混合培养物合成，以便确定关于 DOC 对中链长（mcl-）PHA 生产的影响的机会和差距，这一领域尚未进行详细研究。文献表明，scl-PHA 的生产（还原过程）充当电子汇，使细胞能够在低 DOC 下保持平衡的氧化还原状态。相反，在低 DOC 环境中，脂肪酸从头合成（也是还原过程）不会产生大量的 mcl-PHA，而脂肪酸的 mcl-PHA 合成（氧化过程）可以在低 DOC 环境中得到促进。单体组成、分子量以及聚合物的物理和热性能可能会因 OTR 而发生变化，但在这方面还需要对 scl-PHA 和 mcl-PHA 进行进一步的研究。因此，PHA 生产中生物反应器 OTR 的工艺设计和管理可能取决于聚合物的最终应用，而不是成本考虑。
