Bioremediation of Plastic Pollution

由于合成塑料的发明和随后一次性塑料的广泛采用，塑料污染问题已经成为地方性的问题。目前，每年有480万至1270万吨塑料进入海洋。这些塑料中的一个很大的子集被称为微塑料，由于它们进入了包括人类在内的所有层面的食物链，因此引起了极大的关注。最近，在环境中发现了能够降解塑料成分的微生物，如聚对苯二甲酸乙二酯(PET)，这种能力已经转移到了大肠杆菌中。然而，PETase(PET消化酶)还没有转移到酵母中。酿酒酵母等酵母菌具有适应工业规模恶劣条件的天然能力，能分泌具有生物活性的蛋白质，已被广泛用于合成高滴度的重组蛋白。因此，酵母有可能被用作PETase表达系统，在许多工业和环境环境中降解微塑料。因此，这个项目将着眼于对酿酒酵母进行基因改造，以表达、折叠和分泌PETase。该项目将调查许多不同菌株背景下的PETase活性，并使用数量性状基因座和定向进化来产生最大限度地提高PETase活性同时将毒性降至最低的菌株。这样做的目的是创造一种适合在各种不同环境中降解微塑料中的PET的酵母菌株。

Since the invention of synthetic plastics and subsequent wide spread adoption of single use plastics, the problem of plastic pollution has become endemic. Currently, 4.8 - 12.7 million tonnes of plastic enter the oceans every year. A large subset of these plastics called microplastics are of great concern due to making their way into the food chain at all levels including humans. Recently microorganisms capable of degrading plastic components such as Polyethylene terephthalate (PET) have been identified in the environment and this capability has since be transferred to Escherichia coli. However, PETase (PET digesting enzyme) has yet to be transferred into yeast. Yeast such as S. cerevisiae has a natural ability to harsh industrial-scale conditions, naturally secretes biologically active proteins, and has been widely used for the synthesis of recombinant proteins with high titres. As such yeast holds the potential to be used as a PETase expression system to degrade microplastics in a number of industrial and environmental settings. This project will therefore look into genetically modifying S. cerevisiae to express, fold and secrete PETase. The project will investigate the activity of PETase in many different strain backgrounds and using quantitative trait loci and directed evolution to generate strains that maximise PETase activity while minimising toxicity. This will be done with the aim to create a strain of yeast suitable for the degradation of PET in microplastics in a variety of different settings.