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全球性问题，预计到2050年，将有12亿吨塑料垃圾进入垃圾填埋场或环境中。虽然回收可以让一些塑料获得第二次生命，但并非所有类型的塑料都容易回收，成本可能是一个限制因素，导致只有9%的塑料废物被回收利用。如果塑料不被回收利用，它要么被送到垃圾填埋场，在那里污染土壤，流失污染全球水系统，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。一种环保的替代方法是通过微生物将塑料生物降解成无毒的分解产物，其中一些可以用于下游工业用途，例如聚乙二醇，它有许多用途，包括作为食品和饮料中的消泡剂。人们发现有多种细菌可以降解废塑料，但其中许多细菌的降解速度很慢，在几个月的时间里，塑料的重量只会减少一点点。这方面的一个例子是塑料降解微生物的环境联盟，它能够在6个月内将聚苯乙烯的重量减少约5%。最近的研究集中在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。虽然这些方法取得了一些进步，但这些酶要成为解决塑料垃圾问题的可行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，以提高它们的活性。在这个提议中，我们的目标是采取一种新颖的方法，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群落的表面上，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自己不受环境的影响，并能彼此共享资源和营养。为了形成生物膜，细菌会产生一种叫做胞外多糖的黏液，这种黏液包围着菌群。每个人都遇到过的细菌生物膜的一个很好的例子是牙菌斑。这是一群喜欢在口腔中生长的细菌，所以它们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。在这个提议中，我们计划利用基因工程来利用细菌的这种行为来诱骗塑料降解细菌在废塑料表面形成大的生物膜。在废塑料上形成生物膜有两个主要优点。第一个优点是它增加了废塑料周围塑料降解酶的浓度，酶越多意味着降解越多。另一个主要优点是细菌产生的胞外多糖黏液会阻止酶被冲走。我们已经在实验室里进行了一些初步测试，以证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。我们还用众所周知的塑料食用酶测试了我们的方法，结果表明，生物膜形成水平的增加会导致塑料降解水平的大幅提高。在高风险，高回报的策略中，我们现在想测试我们的方法，针对最常见和最难降解的废塑料，如聚对苯二甲酸乙二醇酯（PET）。我们还想在一个生物反应器中测试这种方法，在这个生物反应器中，细菌被喂食废塑料。我们相信未来；每家每户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.