Advancing the cyanobacterial cell factory: Synechocystis sp. 6803

蓝藻是一种光自养原核生物，能够通过氧合光合作用将光转化为化学能。这种化学能通常被用来促进生长和后代的产生，然而，已经证明，它可以从生长转向，以可再生的方式用于生产有用的碳基化合物，如燃料和药品。聚球藻。6803是一种单细胞、可自然转化、具有完全测序和注释基因组的蓝藻，已成为该领域的模式蓝藻。虽然聚球藻已经成功地生产了各种碳基化合物，但产量远远低于在大肠杆菌或酿酒酵母中实现的产量。改造特定菌株、规模化种植、收获生物量和提取感兴趣的产品的投入成本大大超过了预期产品的价值。缺乏对控制和调控基因表达的基本细胞过程的了解是导致这些低产量的原因。本项目旨在揭示更详细的洞察力，以了解集胞藻的基因组结构、DNA复制机制和基因组拷贝数的调节。6803号。聚球藻是多倍体，每个细胞的基因组拷贝数随生长阶段和环境条件的不同而变化。然而，目前还不清楚基因组拷贝数为什么会波动，以及这一过程是如何调节的。此外，集胞藻的染色体有一个未知的复制来源，这一领域的一些研究表明，被认为普遍存在于原核生物的DNA复制机制在集胞藻中并不是必需的。最后，假设原核生物中的DNA在胞质中自由定位，基因组组织是只有真核生物才有的现象；这一假设尚未得到证实。简单地结构性表达异源代谢途径只会导致遗传不稳定和宿主细胞的代谢负担。控制外源基因的表达是获得所需产品的高产量的关键。通过揭示集胞藻调节其基因组拷贝数、启动DNA复制和组织其基因组的分子过程，这项研究希望为该领域的工作人员提供更好的控制异源基因在集胞藻中表达的方式和时间，从而改进蓝藻细胞工厂的概念。

Cyanobacteria are photoautotrophic prokaryotes capable of converting light into chemical energy via oxygenic photosynthesis. This chemical energy is conventionally used to fuel growth and the generation of progeny however, it has been demonstrated that it can be redirected away from growth and used to generate useful carbon-based compounds such as fuels and pharmaceuticals in a renewable manner. Synechocystis sp. 6803 has become a model cyanobacterium in this field as it is unicellular, naturally transformable and possess a fully sequenced and annotated genome. Whilst a variety of carbon based compounds have been successfully produced in Synechocystis, the yields are significantly less than those achieved in Escherichia coli or Saccharomyces cerevisiae. The input costs of engineering specific strains, growing them at scale, harvesting biomass and extracting the product of interest significantly outweigh the value of the desired product. A lack of understanding of the basic cellular process that control and regulate gene expression is responsible for these low yields.This project aims to reveal a more detailed insight into the genome architecture, mechanisms of DNA replication and the regulation of genome copy number in Synechocystis sp. 6803. It is now well understood that Synechocystis is polyploid and the exact number of genome copies per cell fluctuates depending on the growth phase and environmental conditions. However, it is as of yet unknown why the genome copy number fluctuates and how this process is regulated. Furthermore, the chromosome of Synechocystis has an as of yet undescribed origin of replication and some studies in this area have suggested that the DNA replication machinery thought to be ubiquitous to prokaryotes is not essential in Synechocystis. And finally, it is assumed that DNA in prokaryotes is located freely within the cytosol and that genome organisation is a phenomenon reserved only for eukaryotes; an assumption that has yet to be confirmed. Simply constitutively expressing heterologous metabolic pathways has only resulted in genetic instability and a metabolic burden on the host cell. Control over heterologous gene expression is key to achieving high yields of desired products. By revealing the molecular processes by which Synechocystis regulates its genome copy number, initiates DNA replication and organises its genome, this study hopes to provide those working in this field with greater control over how and when heterologous genes are expressed in Synechocystis, thereby improving the notion of a cyanobacterial cell factory.