Painting with bacteria could capture carbon and yield biofuels for a sustainable energy supply

The Microbiology Society is undertaking a project entitled A Sustainable Future as part of our 75th Anniversary, which aims to highlight the Sustainable Development Goals (SDGs) to our members and empower them to use their research to evidence and impact the goals. Earlier this year, we put a call out to our members to submit case studies in the following three areas: antimicrobial resistance, soil health and the circular economy.

This case study is written by Joseph Keddie, Professor of Soft Matter Physics and Dr Suzie Hingley-Wilson, a Lecturer in Bacteriology, both based at the University of Surrey, UK.  Dr Hingley-Wilson is also a member of the Microbiology Society. This case study relates to the theme of the Circular Economy; an alternative to a traditional linear economy (make, use, dispose), in which we keep resources in use for as long as possible, extract the maximum value from them while in use, then recover and regenerate products and materials at the end of each service life.

A biocoating is a type of water-based paint encapsulating live bacteria. The biocoating holds the bacilli in place and keeps them hydrated and metabolically active. The coating is made like other types of paint, by casting on a surface and simply allowing to dry. Biocoatings can be used on the surfaces of bioreactors, or as biosensors or biocatalysts.  They have many exciting applications including food packaging, bioremediation, and ‘living’ paints for sustainable energy. 

Biocoatings consist of a polymeric layer that encapsulate the bacteria. When inside the coating, the bacteria do not grow or divide, but they can still perform useful functions, such as absorbing toxins or carbon dioxide or emitting gases for use as biofuels. Although other researchers have previously manufactured biocoatings, the rehydrated bacteria did not stay alive for long, which limited their use. The research at the University of Surrey showed that it is necessary for biocoatings to have a permeable structure to allow water and nutrients to enter the biocoating to maintain metabolic activity and to allow by-products to escape.

What findings and solutions were provided by this research?

Researchers at the University of Surrey sought to resolve the issue of permeability in biocoatings, key to the survival of the bacteria within them. They used halloysite, which consists of natural low-cost and microscopic tubes of clay, previously used as a reinforcement for plastic materials.  The tiny halloysite tubes created channels in the biocoating to raise the permeability.

In their fundamental investigations, they used Escherichia coli bacteria as a model organism. Using a specially adapted resazurin reduction assay, they found that E. coli encapsulated in halloysite biocoatings were statistically more likely to stay viable compared to bacteria in the ordinary biocoatings. They determined that a coating made up of 29% halloysite had the best combination of good mechanical strength and high permeability. Importantly, fluorescence microscopy determined that the bacteria remained viable and metabolically active for extended periods of time. In the future, viable bacteria could be used in sustainable processes, as outlined below.

This interdisciplinary project benefits from the combined experience of bacteriologists and soft matter physicists who specialise in polymer colloids, which are the building blocks of the coatings. The team includes Dr Yuxiu Chen and Simone Krings, who divide their time and expertise between the soft matter and bacteriology laboratories at the University of Surrey.

Joseph Keddie, Professor of Soft Matter Physics at the University of Surrey, said: “Our research is an interdisciplinary collaboration. Only when working together could we make a breakthrough in biocoatings. Now that we have discovered a way to maintain metabolic activity of bacteria in the biocoatings, we are ready to develop applications in sustainable energy. We are grateful to The Leverhulme Trust for making the research possible.”

How can this research support the transition to a more sustainable future?

The majority of bacteria are beneficial and without them, many daily processes and life as we know it would be impossible. Maintaining their viability within biocoatings is critical to harnessing their many powers, which could revolutionise applications in sustainable energy. Current research at the University of Surrey is encapsulating cyanobacteria in biocoatings. These micro-organisms will be able to undergo photosynthesis in coatings, capturing CO₂ and reducing the carbon footprint of processes. Another potential application is to use bacteria that are engineered to produce hydrogen gas, which will be used as a biofuel for sustainable energy production by fuel cells.

About the authors

Professor Joseph Keddie is a Professor of Soft Matter Physics and Dr Suzie Hingley-Wilson is currently a Lecturer in Bacteriology, both at the University of Surrey. This research was funded by a Research Project Grant from The Leverhulme Trust. The research was conducted by Dr Phil Chen (University of Surrey) and Simone Krings (University of Surrey) and in collaboration with Joshua Booth (University of Warwick) and Professor Stefan Bon (University of Warwick). The authors would like to thank N. Meredith from the University of Surrey for her help. More information about Dr Hingley-Wilson’s and Professor Keddie’s research are available here and here.