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February 20, 2018

Bacteria Out to Paint the Town

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    The image shows a colony of the Flavobacterium IR1, 2 cm in diameter, growing on a nutrient agar plate. The cells in the colony are highly organized, thus forming a 2D photonic crystal that interferes with light. This results in structurally colored, bright, and angle-specific hues with a concentric ring pattern, indicating subtle changes in organization. The older cells of IR1 in the colony center are more disorganized and therefore lose color. IR1 can be genetically modified from this wild-type strain to create new, living photonic structures. [University of Cambridge]

    “Going green” may have just taken on new meaning, with respect to paint colors at least, as a new study from a collaboration between the University of Cambridge and Dutch company Hoekmine BV shows how genetics can change the color, and appearance, of certain types of brightly colored bacteria. The team of investigators was able to unlock the genetic code behind some of the brightest and most vibrant colors in nature. Findings from the new study—published recently in Proceedings of the National Academy of Sciences (PNAS) in an article entitled “Living colors: Genetic Manipulation of Structural Color in Bacterial Colonies”—open the possibility of harvesting these bacteria for the large-scale manufacturing of nanostructured materials. Biodegradable, nontoxic paints could be “grown” and not made.

    "It is crucial to map the genes responsible for the structural coloration for further understanding of how nanostructures are engineered in nature," explained lead study investigator Villads Egede Johansen, Ph.D., a postdoctoral researcher in the department of chemistry at the University of Cambridge. "This is the first systematic study of the genes underpinning structural colors—not only in bacteria but in any living system."

    This is the first study of the genetics of structural color—as seen in butterfly wings and peacock feathers—and paves the way for genetic research in a variety of structurally colored organisms.

    In the current study, the researchers focused on Flavobacterium, a type of bacteria that packs together in colonies that produce striking metallic colors, which come not from pigments, but from their internal structure. Interestingly, these structures reflect light at certain wavelengths, and scientists are still puzzled as to how these intricate structures are genetically engineered by nature.

    "We mapped several genes with previously unknown functions, and we correlated them to the colonies' self-organizational capacity and their coloration," noted senior study investigator Villads Egede Johansen, Ph.D..

    The researchers compared the genetic information to optical properties and anatomy of wild-type and mutated bacterial colonies to understand how genes regulate the color of the colony.

    By genetically mutating the bacteria, the scientists were able to change their dimensions or their ability to move, which altered the geometry of the colonies. By changing the geometry, they changed the color. They changed the original metallic green color of the colony in the entire visible range from blue to red. They were also able to create duller coloration or make the color disappear 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," concluded co-senior author Silvia Vignolini, Ph.D., a reader in chemistry and biomaterials at the University of Cambridge. "We see potential in the use of such bacterial colonies as photonic pigments that can be readily optimized for changing coloration 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 color and appearance we want!"


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