Iridescent bird in forest

Natural iridescence study could allow metallic coatings to be grown from bacteria

Image credit: Dreamstime

A University of Cambridge team has probed the genes of intensely coloured bacteria, opening up the possibility of using this bacteria to “grow” coatings on an industrial scale.

Structural colour is a biological phenomenon which gives way to the intense iridescent colours of peacock feathers and beetle shells. First observed by Isaac Newton and his rival genius Robert Hooke, it is caused by the interference of light with microscopic structured surfaces in animals, plants and other organisms, causing certain wavelengths of light to be reflected.

These naturally engineered structures have inspired the design of manmade objects, such as colour-changing nanoparticles, which work even when embedded in other materials.  

For the first study of the genetics of structural colour, the Cambridge researchers teamed up with Hoekmine BV, a Dutch company, to look into how genetic differences can cause changes in the colour and appearance of certain bacteria: Flavobacterium.

Colonies of flavobacterium tend to appear a metallic green thanks to their microscopic structure causing light to be reflected in a certain manner.

“It is crucial to map the genes responsible for the structural colouration for further understanding of how nanostructures are engineered in nature,” said Dr Villads Egede Johansen, an expert in bio-inspired photonics at the university’s Department of Chemistry.

“This is the first systematic study of the genes underpinning structural colours, not only in bacteria but in any living system.”

In order to understand how the bacteria’s genetic material affects the apparent colour of the colony, the researchers compared the genes, anatomy and colouration of wild bacteria to those of engineered bacteria.

Through small modifications of genes with previously unknown functions, the researchers were able to adapt the geometry of the bacteria, causing the colony to re-organise itself and switch to any other colour of the rainbow, to lose its metallic sheen, or to lose all colour entirely.

“From an applied perspective, this bacterial system allows us to achieve tuneable living photonic structures that can be reproduced in abundance, avoiding traditional nanofabrication methods,” said senior co-author Dr Silvia Vignolini, who studies the optical properties of natural and bio-mimetic materials at Cambridge.

“We see a potential in the use of such bacterial colonies as photonic pigments that can be readily optimised for changing colouration under external stimuli and that can interface with other living tissues, thereby adapting to variable environments. The future is open for biodegradable paints on our cars and walls, simply by growing exactly the colour and appearance we want.”

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