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

背景：目前乙烯是由乙烷蒸气裂解产生的，乙烷裂解产生大量二氧化碳，导致全球变暖。2000年，蒸汽裂解的一次能源消耗量为30亿吉焦耳，二氧化碳排放量约为2亿吨。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。寻找一种可持续的或碳中性的乙烯生产替代品是当务之急。蓝藻是革兰氏阴性光合原核生物。研究人员此前曾试图通过在蓝藻--细长聚球藻中异源表达EFe基因来从二氧化碳合成乙烯。PCC7942和聚球藻sp.PCC 6803，结果好坏参半。目的：该项目的目的是将蓝藻作为生产乙烯等碳氢化合物产品的平台。紫丁香假单胞菌乙烯形成酶EFe基因的表达聚球藻中的菜单胞菌。PCC6803，导致了乙烯的连续产生。我们现在正在通过定向进化和代谢工程来提高产量。作为这一过程的一部分，我们希望设计一种利用植物的阳离子途径来生产乙烯的合成途径。这为在蓝藻中实施一种新的途径并将乙烯产生与生长联系起来提供了一个令人兴奋的机会。乙烯是由1-氨基环丙烷-1-羧酸(ACC)有效地生物合成的(周等人，2002)，而1-氨基环丙烷-1-羧酸本身是从蛋氨酸衍生而来的，作为阳环的一个分支(Wang等人，2002)。这个过程在能量上是有效的，因为它保留了高能的蛋氨酸硫醚键。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)转化为乙烯释放氰甲酸，氰甲酸自发脱羧释放氰化氢，氰化氢主要通过CAS途径解毒(Machingura等人，2016)。这一途径的实施将为蓝藻中氰化物的解毒提供一种机制。培训：该项目将允许在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可转让的技能，在日益增长的生物经济中，雇主非常珍视这些技能。该项目还将提供几份影响较大的出版物。这一翻译项目将在位于诺丁汉的BBSRC/EPSRC合成生物学研究中心(SBRC)内进行，该中心由70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GB。

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.