When a Hoekmine BV team unexpectedly discovered that they had isolated a previously unknown, brilliantly green coloured strain of bacteria, they contacted researchers at University of Cambridge to investigate this phenomenon further. According to Villads Egede Johansen, co-first author of this work, "from that point onwards, we were both driven to explore what can be done to alter and influence this system".

The ensuing experimental work represents the first systematic study linking genetic markers to structural colour, with the hope that more studies will now be sparked in this direction. Striking examples of structural colour, which refers to colour that is not obtained through pigmentation, are found in natural phenomena such as butterfly wings and peacock feathers. Genetic control of macroscopic properties such as colour opens the door to an almost limitless number of material and device fabrication options.

From bacteria to sensors

The bacteria used as a model system in this research is the Flavobacterium IR1 strain. These are rod-shaped bacteria that are able to pack together through gliding and growing mechanisms. Under different genetic and environmental conditions, Flavobacterium colonies form ordered nanostructures that interfere with light to give distinctive bright green, yellow, blue and red iridescent colorations, spanning the entire visible spectrum.

The iridescent colours are highly distinctive, meaning they have great potential for use as cheap and effective chemical sensors. For example, the bacteria could be genetically engineered to lose colour upon exposure to a specific chemical compound. This builds on existing concepts such as using sensors to "sniff out" drug production in sewers and using bacteria to detect explosives such as landmines. Other applications being considered are biodegradable paints and colorants, giving rise to the idea that we could even grow our own customized paints from different bacterial colonies.

A brightly irridescent future

To drive this research forwards, it is imperative to further understand the biological functions of the packing that leads to this distinctive expression of colour. The researchers were the first to link these packing mechanisms to both optical response, or manifestation of colour, and to certain genetic markers.

However, the eternal ‘nature versus nurture’ issue must also be considered, as it was observed that not only do genetic markers influence how the colonies exhibit colour, environmental changes have a distinctive effect. Fucoidan is a sulphated polymer derived from brown algae that the scientists found enhances the structural coloration. This discovery highlights the need for further research in this field to fully understand genetically modified colour.

Using genetics to alter and influence the material response of biological systems paves the way forward to a bright and shimmering future, filled with biodegradable, eco-friendly nanofunctional materials grown to fulfil our planet’s ever-increasing demands on resources.

Full details of the research are reported in Proceedings of the National Academy of Sciences DOI: https://doi.org/10.1073/pnas.1716214115