Institute of Molecular Enzyme Technology, Heinrich-Heine-University Düsseldorf, Forschungszentrum Jülich, 52425 Jülich, Germany.
Institute of Molecular Enzyme Technology, Heinrich-Heine-University Düsseldorf, Forschungszentrum Jülich, 52425 Jülich, Germany.
Metab Eng. 2017 Jul;42:145-156. doi: 10.1016/j.ymben.2017.06.009. Epub 2017 Jun 20.
In natural habitats, microbes form multispecies communities that commonly face rapidly changing and highly competitive environments. Thus, phenotypic heterogeneity has evolved as an innate and important survival strategy to gain an overall fitness advantage over cohabiting competitors. However, in defined artificial environments such as monocultures in small- to large-scale bioreactors, cell-to-cell variations are presumed to cause reduced production yields as well as process instability. Hence, engineering microbial production toward phenotypic homogeneity is a highly promising approach for synthetic biology and bioprocess optimization. In this review, we discuss recent studies that have unraveled the cell-to-cell heterogeneity observed during bacterial gene expression and metabolite production as well as the molecular mechanisms involved. In addition, current single-cell technologies are briefly reviewed with respect to their applicability in exploring cell-to-cell variations. We highlight emerging strategies and tools to reduce phenotypic heterogeneity in biotechnological expression setups. Here, strain or inducer modifications are combined with cell physiology manipulations to achieve the ultimate goal of equalizing bacterial populations. In this way, the majority of cells can be forced into high productivity, thus reducing less productive subpopulations that tend to consume valuable resources during production. Modifications in uptake systems, inducer molecules or nutrients represent valuable tools for diminishing heterogeneity. Finally, we address the challenge of transferring homogeneously responding cells into large-scale bioprocesses. Environmental heterogeneity originating from extrinsic factors such as stirring speed and pH, oxygen, temperature or nutrient distribution can significantly influence cellular physiology. We conclude that engineering microbial populations toward phenotypic homogeneity is an increasingly important task to take biotechnological productions to the next level of control.
在自然栖息地中，微生物形成多物种群落，这些群落通常面临快速变化和极具竞争力的环境。因此，表型异质性已进化为一种内在的重要生存策略，以获得比共居竞争者更高的整体适应度优势。然而，在定义明确的人工环境中，如小型到大型生物反应器中的单一培养物，细胞间的变异被认为会导致产量降低和过程不稳定。因此，朝着表型均一性工程微生物生产是合成生物学和生物过程优化的一个极具前景的方法。在这篇综述中，我们讨论了最近的研究，这些研究揭示了在细菌基因表达和代谢产物生产过程中观察到的细胞间异质性以及所涉及的分子机制。此外，还简要回顾了当前的单细胞技术，探讨了它们在探索细胞间变异方面的适用性。我们强调了减少生物技术表达装置中表型异质性的新兴策略和工具。在这里，通过对菌株或诱导剂进行修饰并结合细胞生理学操作，来实现使细菌种群均匀化的最终目标。通过这种方式，大多数细胞都可以被强制进入高生产力状态，从而减少在生产过程中消耗有价值资源的低生产力亚群。改造摄取系统、诱导剂分子或营养物质是减少异质性的有效工具。最后，我们解决了将均匀响应的细胞转移到大规模生物过程中的挑战。源于搅拌速度、pH 值、氧气、温度或营养分布等外在因素的环境异质性会显著影响细胞生理学。我们得出的结论是，朝着表型均一性工程微生物种群是将生物技术生产提升到下一个控制水平的一个日益重要的任务。
