Engineering synthetic pathways to bio-ethylene production in Cyanobacteria sp.

背景：乙烯目前是由乙烷的蒸汽裂解产生的，其产生大量的CO2，导致全球变暖。2000年，蒸汽裂解的一次能源使用量为30亿千兆焦耳，排放了约2亿吨二氧化碳。乙烯是最常见的塑料聚乙烯的单体，全球年产量约为8000万吨。找到一种可持续的或碳中和的乙烯生产替代品势在必行。蓝细菌是革兰氏阴性光合原核生物。研究人员以前曾试图通过在蓝细菌，细长聚球藻属PCC 7942和集胞藻属PCC 6803中异源表达efe基因来从CO2中产生乙烯，结果好坏参半。目的：该项目的目的是将蓝细菌作为生产乙烯等碳氢化合物产品的平台。大肠杆菌乙烯形成酶基因的表达。Phaseolicola在集胞藻PCC 6803中引起乙烯的连续产生。我们现在正在通过定向进化和代谢工程来提高产量。作为该过程的一部分，我们希望利用植物的Yang途径设计乙烯生产的合成途径。这提供了一个令人兴奋的机会，实施一个新的途径，蓝藻和链接乙烯生产的增长。乙烯由1-氨基环丙烷-1-羧酸（ACC）有效地生物合成（Zhou等人，2002），其本身衍生自作为杨循环分支的甲硫氨酸（Wang et al.，2002年）。该过程在能量上是有效的，因为它保留了高能甲硫氨酸硫醚键。该途径利用SAM合成酶、ACC合成酶和ACC氧化酶。1-氨基-环丙烷-1-羧酸（ACC）转化为乙烯释放氰基甲酸，氰基甲酸自发地脱羧以释放氰化氢，氰化氢主要通过CAS途径解毒（Machingura等人，2016）。这一途径的实施将提供一个机制，解毒蓝藻氰化物。培训内容：该项目将允许在一个独特的多学科环境中进行培训，包括基因组工程，气体发酵，合成生物学，尖端分子生物学和系统生物学建模。该项目将为学生提供大量的可转移技能，在不断增长的生物经济中受到雇主的高度重视。该项目还将提供若干影响力大的出版物。该翻译项目将在诺丁汉的BBSRC/EPSRC合成生物学研究中心（SBRC）内进行，该中心由70多名研究生和博士后研究人员组成（www.clostron.com/people.php），目前的预算为2700万英镑。

Background: Ethylene is currently produced from the stream cracking of ethane which produces large quantities of CO2, contributing to global warming. In 2000, steam cracking had a primary energy use of 3 billion Gigajoules and accounted for approximately 200 million tons of CO2 emissions. Ethylene is the monomer for the most common plastic, polyethylene, and annual global production is approximately 80 million tons. Finding a sustainable or carbon neutral alternative to ethylene production is imperative. Cyanobacteria are Gram-negative photosynthetic prokaryotes. Researchers have previously attempted to produce ethylene from CO2 through heterologous expression of the efe gene in the cyanobacteria, Synechococcus elongates sp. PCC 7942 and Synechocystis sp. PCC 6803, with mixed results. Aim: The aim of this project is to engineer cyanobacteria as a platform for the production of hydrocarbon-based products such as ethylene. Expression of the efe gene encoding the ethylene-forming enzyme from Pseudomonas syringae pv. Phaseolicola in Synechocystis sp. PCC 6803, led to continuous ethylene production. We are now in the process of improving production through directed evolution and metabolic engineering. As part of this process we would like to engineer a synthetic pathway for ethylene production utilising the Yang pathway from plants. This provides an exciting opportunity to implement a novel pathway in cyanobacteria and link ethylene production to growth. Ethylene is efficiently biosynthesized from 1-aminocyclopropane-1-carboxylic acid (ACC) (Zhou et al., 2002), which is itself derived from methionine as a branch of the Yang cycle (Wang et al., 2002). This process is energetically efficient as it preserves the high-energy methionine thioether bond. This pathway utilises SAM synthetase, ACC synthase and ACC oxidase. The conversion of 1-amino-cyclopropane-1-carboxylic acid (ACC) to ethylene releases cyanoformic acid, which spontaneously decarboxylates to release hydrogen cyanide, which is principally detoxified by the CAS pathway (Machingura et al., 2016). The implementation of this pathway will provide a mechanism for detoxifying cyanide in cyanobacteria. Training: The project will allow for training in a unique multidisciplinary environment, incorporating genomic engineering, gas fermentation, synthetic biology, cutting edge molecular biology and systems biology modelling. The project will providing the student with a vast array of transferable skills, highly prized by employers in the growing bio-economy. The project will also provide several high impact publications. This translational project will be carried out within the BBSRC/EPSRC Synthetic Biology Research Centre (SBRC) at Nottingham which comprises 70+ graduate and postdoctoral researchers (www.clostron.com/people.php) and a current budget of £27M.