Engineering sustainable pathways to plastic recycling in Cyanobacteria

Plastic usage will double by 2036, yet >70% is unrecyclable and >94% is still produced from virgin hydrocarbons. Despite growing social momentum for a plastics circular economy, re-processing of mixed plastic waste (MPW) is extremely challenging. Waste-to-energy (W2E) technology offers a steppingstone technology, extracting value from MPW but at high environmental cost (CO2 production) and is a fundamentally open-loop process (low on the waste hierarchy). The remaining plastic waste sits in the environment or ends up in landfill where it can take up to 500 years to decompose, leaching toxic chemicals into the ground. Traditional plastics such as the polyester poly (ethylene terephthalate) (PET) are made from oil based raw materials. PET makes up almost one sixth of the world's annual plastic production of 311m tons. Around 41m tons of PET was produced in 2013 and this is projected to increase to 73m tons by 2020. PE production currently exceeds 100 million tons accounting for 34% of the plastics market, with worldwide usage of plastic bags alone
exceeding 1 trillion a year. It is imperative that we find an efficient and green solution to tackle the global plastic problem.

Cyanobacteria are exemplars of the first microorganisms capable of oxygenic photosynthesis and capable of fixing 1.83 kg of CO2 per 1 kg of biomass.

This project aims to utilise waste plastics such as PET and PE and produce biodegradable plastic and high value chemicals in a cyanobacterial chassis.

Objectives
The PhD project will have three main objectives; the first objective being to generate a strain capable of enhanced plastic degradation through the expression of novel lipases and hydrolases in cyanobacteria. These strains will be fully characterised utilising a wide variety of techniques to monitor the physiological state of the cell, plastic degradation and biofilm formation on the plastic.
The properties of the plastic will also be assessed using NMR and FT-IR. Engineered strains will then be subject to metabolomic characterisation (metabolic phenotyping) to estimate intra and extracellular metabolic fluxes. Conventional LC-MS-based metabolomics and stable isotope-assisted metabolic pathway profiling, coupled with 13C flux analysis will be utilised to predict in vivo enzyme reaction rates, unravelling key metabolism and providing exemplar kinetic data, allowing for the development of designer strains with improved plastic degradation.
The second objective will focus on utilising these strains as chassis to produce 2,5-PDCA from PET, which is a bioplastic building block. Metabolic engineering utilising CRISPR and CRISPRi coupled with metabolomic analysis will allow flux to be diverted to 2,5-PDCA production. This will then be utilised to produce bioplastics in collaboration with Biome Bioplastics (industrial collaborator).
The third objective will focus on isolating novel cyanobacterial strains from the environment particularly environments contaminated by plastic pollution. Strains will be isolated on both PET and PE and characterised via genomics, transcriptomics, proteomics and metabolomics to identify novel enzymes which can be utilised in Obj. 1 and 2.

The student will receive dedicated mentoring from the supervisory team and will benefit from their substantial expertise and the multidisciplinary nature of the project.

References to learn more:
1. Danso, D., Chow, J., Streit, W. R. (2019) Plastics: Environmental and Biotechnological Perspectives on Microbial Degradation. Applied and Environmental Microbiology, 85(19),
e01095-19.
2. Sarmah, P., Rout, J. (2019) Cyanobacterial degradation of low-density polyethylene (LDPE) by Nostoc carneum isolated from submerged polyethylene