Stemming the tide: plastics at Portsmouth

Although the stability of these polymers is a major factor in their usefulness, poor waste management at a global level has led to an accumulation of plastic in virtually all environmental systems. The widespread damage was brought vividly to the centre of public attention in Blue Planet II, the BBC documentary series narrated by Sir David Attenborough. Media attention is having a positive effect, with the general public demanding a better understanding of the fate of plastics in the environment and the need for more innovative ways of reducing, reclaiming and recycling plastics. This public focus has resulted in the UK government setting an ambitious 70% target for the recycling of plastic packaging by 2025.

Recently, microbiologists have isolated and identified a new species of bacteria capable of degrading plastics, Ideonella sakaiensis. At the Centre of Enzyme Innovation at the University of Portsmouth, Professor John McGeehan (CEI Director) and his group have been working with I. sakaiensis to solve the crystal structure of the enzyme responsible and, via mutation studies, improved the function of the PETase enzyme that is capable of digesting common plastics. This approach has great financial and environmental merit, as mixed-waste plastics could be returned to their original monomer constituents and upcycled to potentially higher-value products. At the CEI, this approach is now being applied to a number of other common plastic waste products and the enzyme production scaled up for possible industrial applications. Producing a range of microorganisms or enzymes that could degrade plastics (and especially mixed plastic waste streams) into constituent monomers, is a highly attractive solution.

As the University of Portsmouth is situated on the coast, the impact of plastics on the coastal environment is very apparent. Ongoing studies are focused on the environmental impact and global distribution of plastics using citizen science in innovative ways, such as The Big Microplastics Survey. Although the distribution of plastics is important, as with all solid surfaces in the aquatic environment, plastics and microplastics provide surfaces for high levels of microbial colonisation and possible biofilm formation. We have been examining the diversity of microbes attached to microplastics released from sewage treatment facilities and in other aquatic environments. As expected, many microbes attach readily and can stay attached for long periods of time. This attachment has a number of implications for pathogen dispersal and survivability in the environment. A number of studies are underway to better understand the effects of microbial-contaminated microplastics in food chains and how they impact environmental health. For example, an ongoing laboratory study has been examining the effects of adding microplastics with different microbial loads to oysters and tracking their health and mortality in comparison with non-contaminated plastic exposure. Unsurprisingly, plastics with microbial contamination appear to have more negative effects on oyster health and mortality than non-contaminated microplastics. As Sir David highlighted in his SfAM Fellowship acceptance speech, as microbiologists we are central to finding new organisms capable of complex polymer degradation and better understanding the effects of microplastics on food chains and environmental systems. It is an exciting research area to be involved in!