Sustainable Photonic Pigments Made of Bacteria

Pigments are ubiquitous components of our everyday life as they are used for colouring several materials including paint, ink, fabrics, food and cosmetics. However, the manufacturing process of conventional pigments places a high burden on the environment, as it consumes high energy and resources, among them, irreplaceable petroleum. Moreover, many traditional pigments pose high risks for human health as they contain heavy metals or inorganic particles.

Additionally, their production requires hazardous substances and mining for mineral pigments, in particular in developing countries, have devastating effects both for the environment and society.

Our project aims at the development of new bio-based pigments that are sustainable, bio-compatible and easily scalable for mass production. In particular, we want to develop a methodology to exploit bacteria as building blocks for pigments. The vision of this research proposal is to harness the ability of bacteria to show bright colouration as a result of the physical organisation of cells within colonies.

Their colouration is therefore not caused by pigmentation, but it is due to sub-micron organisation, which function as photonic crystals reflecting light only at specific wavelengths. This phenomenon is called "structural colour" and is at the base of the colouration of many living organisms (e.g. the peacock feathers or morpho butterfly wings).

Depending on the size of the nanostructures, a specific colour is reflected and, depending on the regularity of the patterned areas, the effect can be matte (angularly independent ) or metallic iridescent (strongly affected by the viewing angle).

Recently, in collaboration with the SME Hoekmine BV, under the remit of BBSRC-funded research, we show that we can genetically modify marine flavobacteria. We were able to change their organisation and their motility, thereby altering their interactions with lights. As a consequence, we were able to change their colour and to tune it in the entire visible spectrum from blue to red.

The ambition of this proposal is to move forward from this proof-of-concept and produce bio-based commercial pigments to replace synthetic counterparts in paints and beyond. We foresee this bacteria-based pigment production to be entirely bio-compatible as the bacterial strains, all consumables for bioengineering, fermentation, and the supporting substrates are conceived to be safe and fully biodegradable.

The project has the potential to fulfil an ever-growing market and consumer demand of bio-materials, in the effort to establish a more sustainable and circular economy. For this reason, it has received a strong endorsement from a vast network of pigment manufacturers interested in the outcome of this work. Using bacteria to make pigments is indeed very promising for producers, as this strategy is expected to lower costs by producing bacteria in the desired quantities, other than reducing the ecological impact and health risks associated with the synthetic pigments.

Also, the produced pigments are expected to present the significant advantage of increased colour stability, as the colouration does not depend on the chemical composition but on the physical properties of the colonies, making the colour very stable against bleaching. Finally, we believe that the methodologies developed in this project pave the way towards the exploitation of bacteria for the fabrication of new bio-based, renewable materials.

We foresee these materials to be relevant to several commercial applications beyond the paint and coating sectors (e.g., cosmetics, food additives, and drug delivery) and to have enormous societal and environmental benefits.