Genetic manipulation of structural color in bacterial colonies

Abstract

<p id="d7555035e303">We demonstrate the genetic modification of structural color in a living system by using bacteria Iridescent 1 (IR1) as a model system. IR1 colonies consist of rod-shaped bacteria that pack in a dense hexagonal arrangement through gliding and growth, thus interfering with light to give a bright, green, and glittering appearance. By generating IR1 mutants and mapping their optical properties, we show that genetic alterations can change colony organization and thus their visual appearance. The findings provide insight into the genes controlling structural color, which is important for evolutionary studies and for understanding biological formation at the nanoscale. At the same time, it is an important step toward directed engineering of photonic systems from living organisms. </p><p class="first" id="d7555035e306">Naturally occurring photonic structures are responsible for the bright and vivid coloration in a large variety of living organisms. Despite efforts to understand their biological functions, development, and complex optical response, little is known of the underlying genes involved in the development of these nanostructures in any domain of life. Here, we used <i>Flavobacterium</i> colonies as a model system to demonstrate that genes responsible for gliding motility, cell shape, the stringent response, and tRNA modification contribute to the optical appearance of the colony. By structural and optical analysis, we obtained a detailed correlation of how genetic modifications alter structural color in bacterial colonies. Understanding of genotype and phenotype relations in this system opens the way to genetic engineering of on-demand living optical materials, for use as paints and living sensors. </p>