Using synthetic biology to manipulate bacterial social behaviours to maximise the microbial degradation of environmental waste plastics.

塑料污染是一个日益严重的世界性问题，预计到2050年，将有120亿吨塑料垃圾进入垃圾填埋场或环境中。虽然回收可以给一些塑料带来第二次生命，但并不是所有的塑料类型都很容易回收，成本可能是一个限制因素，导致只有9%的塑料垃圾被回收。如果不回收塑料，它要么被送到垃圾填埋场，在那里污染土壤和径流污染全球水系，要么被焚烧，释放有毒烟雾，增加碳排放。塑料污染正在破坏动物的环境，一直到微生物，最终导致生态系统崩溃。一种环境友好的替代方案是由微生物将塑料生物降解成无毒的分解产品，其中一些可用于下游工业用途，如聚乙二醇，它有许多用途，包括在食品和饮料中用作消泡剂。已经发现多种细菌可以降解废旧塑料，然而其中许多细菌的作用速度很慢，导致塑料重量在几个月内只有很小的减轻。这方面的一个例子是一个塑料降解菌的环境联盟，它能够在6个月内使聚苯乙烯的重量减少~5%。最近的研究重点是鉴定这些细菌和真菌产生的能够分解废塑料的酶，并探索是否可以对这些酶进行修饰，以提高它们降解废塑料的能力。虽然这些方法已经产生了一些改进，但这些酶距离成为解决塑料垃圾问题的可行解决方案还有很长的路要走。目前该领域的大多数研究都集中在优化塑料食用酶本身以提高其活性。在这项提议中，我们的目标是采取一种新的方法，通过改变细菌的行为来探索活动优化的前沿，以提高它们降解塑料的能力。细菌喜欢附着在被称为生物膜的社区的表面，因为就像生活在村庄、城镇或城市的人一样，生物膜中的细菌能更好地保护环境，并可以相互分享资源和养分。为了建立生物膜，细菌产生一种叫做胞外多糖的粘液，它包围着群落。每个人都在某种程度上遇到过的细菌生物膜的一个很好的例子是牙菌斑。这是一个喜欢在口腔中生长的细菌群落，所以附着在我们的牙齿上，形成一层生物膜，帮助它们留在这个环境中。在这项提案中，我们计划利用细菌的这种行为，使用基因工程来诱使塑料降解细菌在废塑料表面形成巨大的生物膜。在废旧塑料上形成生物膜有两大好处。第一个好处是它增加了废塑料周围的塑料降解酶的浓度，酶越多意味着降解越多。另一个主要的好处是，细菌产生的胞外多糖粘液将阻止酶被冲走。我们已经在实验室进行了一些初步测试，以表明利用基因工程我们可以增加废塑料上细菌生物膜的形成水平。我们还使用众所周知的塑料进食酶测试了我们的方法，结果表明，增加生物膜形成的水平会导致塑料降解水平的大幅增加。在一个高风险、高回报的策略中，我们现在想要测试我们的方法针对最常见和最难降解的废塑料，如聚对苯二甲酸乙二酯(PET)。我们还想在生物反应器中测试这种方法，在那里细菌被喂入废塑料。我们相信未来；每个家庭都可以拥有自己的微生物塑料降解生物反应器，这项研究可能是实现这一目标的第一步。

Plastic pollution is a growing worldwide problem, with 12,000 million metric tonnes of plastic waste predicted to be in landfill or the environment by 2050. Whilst recycling can give a second life to some plastic, not all plastic types are easily recycled and cost can be a limiting factor, resulting in only 9% of plastic waste having ever been recycled. If plastic is not recycled, it is either sent to landfill where it pollutes the soil and run off pollutes the global water systems, or it is incinerated, releasing toxic fumes and adding to carbon emissions. Plastic pollution is damaging the environments of animals all the way down to microbes, ultimately leading to ecosystem collapse. An environmentally friendly alternative is biodegradation of plastic by microorganisms into non-toxic breakdown products, some of which can be valorised with downstream industrial uses, such as polyethylene glycol, which has many uses including acting as an anti-foaming agent in food and drinks. Multiple species of bacteria have been found to degrade waste plastic, however many of these act at a slow rate resulting in only a small reduction in plastic weight over a period of months. An example of this is an environmental consortia of plastic degrading microorganisms which was able to decrease polystyrene weight by ~5% in 6 months. Recent research has focused on identifying the enzymes produced by these bacteria and fungi that are capable of breaking down waste plastic and exploring if these enzymes can be modified to increase their ability to degrade waste plastic. While these approaches have yielded some improvements, these enzymes are still a long way off being a viable solution to tackling the plastic waste problem. The majority of research in the field is currently focused on optimising the plastic eating enzymes themselves to improve their activity. In this proposal we aim to take a novel approach, exploring the frontiers of activity optimisation by modifying how bacteria behave, to increase their ability to degrade plastic. Bacteria like to attach to surfaces in communities called biofilms because, just like people who live villages, towns or cities, bacteria in biofilms are better protected from the environment and can share resources and nutrients with each other. To build a biofilm, bacteria produce a slime called an exopolysaccharide which surrounds the community. A good example of a bacterial biofilm that everyone has encountered at some point is dental plaque. This is a community of bacteria who like to grow in the mouth, so attach to our teeth and form a biofilm to help them stay in this environment. In this proposal we plan to harness this behaviour of bacteria using genetic engineering to trick plastic degrading bacteria into forming large biofilms on the surface of waste plastic. Forming a biofilm on waste plastic has two major advantages. The first advantage is that it increases the concentration of plastic degrading enzyme around the waste plastic and the more enzyme means the more degradation. The other major advantage is that the exopolysaccharide slime being produced by the bacteria will stop the enzymes from being washed away. We have performed some preliminary tests in the lab to show that using genetic engineering we can increase the levels of bacteria biofilm formation on waste plastic. We have also tested our approach using well-known plastic eating enzymes and shown that increasing the levels of biofilm formation leads to a major increase in the levels of plastic degradation. In a high risk, high reward strategy we now want to test our approach against the most common and difficult to degrade waste plastics such as Polyethylene terephthalate (PET). We also want to test this approach in a bioreactor where bacteria are fed waste plastic. We believe in the future; every house could have their own microbial plastic degrading bioreactor and this research could be the first steps in making this a reality.