Being one of the least recycled plastics, polystyrene is a notorious plastic pollutant with less than 2% of its produced volume recycled. While it is also a surprisingly inert polymer, with a degradation lifespan of up to a million years, its bad recycling reputation mainly comes from the fact that the recycling of its most commonly produced form seems to be economically inefficient.
The expanded form of polystyrene (commonly referred to as styrofoam) unlike other plastics easily erodes down in landfills due to its lightweight properties, making it easily air-transferrable and able to reach kilometric distances, mostly ending up in the ocean.
Figure 1: Eroded styrofoam contaminates areas to a much larger extent than other plastics do, making it more recognizable as a food to fish, while being difficult to clean out.
We aim to degrade polystyrene in two stages; the first one being a chemical dissolving process of polystyrene to its styrene monomers and the second one being the feeding of the styrene to our genetically engineered bacterial cultures.
The main degradation of styrene will be achieved by using an aromatic compound degradation pathway found in Pseudomonas putida F1 strain. This pathway is effective in providing the organism P. putida to degrade and incorporate aromatic hydrocarbons such as toluene and benzene as nutritious sources of carbon to the cell. Because styrene seems structurally similar to the hydrocarbons of the tod pathway, our research is focusing on modifying the enzymes of the pathway to metabolise styrene in almost the same manner as it would for toluene and others. Some studies have in fact already proved that the enzymes in the degradation of toluene are able to recognise styrene as a substrate.
Figure 2: Proposed tod operon pathway on styrene.
TodE and its action on styrene have been investigated before, yielding results that show that an intermediate of styrene breakdown called 3-vinylcatechol is capable of inactivating TodE. We will analyse the TodE gene more closely using bioinformatics with the hopes of altering the active site to better fit the intermediate 3-vinylcatechol, along with overexpression of TodE to speed up the catalysis. Although TodF has already been registered as a BioBrick by Leicester 2013, this year we will attempt to modify their BioBrick to suit the intermediates of styrene, as TodF is an important stage in the tod pathway.
Another focus part of human practices we plan to educate local schools and their pupils on the issue of plastic waste and the use of synthetic biology as a universal problem solver. We also aim to spread awareness through social media and collaborating with other scientists in order to responsibly use plastics in laboratories.