Deletion of the moe A gene in Flavobacterium IR1 drives structural color shift from green to blue and alters polysaccharide metabolism

Structural colors (SC), generated by light interacting with nanostructured materials, is responsible for the brightest and most vivid coloration in nature. Despite being widespread within the tree of life, there is little knowledge of the genes involved. Partial exceptions are some Flavobacteriia in which genes involved in a number of pathways, including gliding motility and polysaccharide metabolism, have been linked to SC. A previous genomic analysis of SC and non-SC bacteria suggested that the pterin pathway is involved in the organization of bacteria to form SC. Thus here, we focus on the moe A molybdopterin molybdenum transferase. When this gene was deleted from Flavobacterium IR1, the knock-out mutant showed a strong blue shift in SC of the colony, different from the green SC of the wild-type. The moe A mutant showed a particularly strong blue shift when grown on kappa-carrageenan and was upregulated for starch degradation. To further analyze the molecular changes, proteomic analysis was performed, showing the upregulation of various polysaccharide utilization loci, which supported the link between moe A and polysaccharide metabolism in SC. Overall, we demonstrated that single-gene mutations could change the optical properties of bacterial SC, which is unprecedented when compared to multicellular organisms where structural color is the result of several genes and can not yet be addressed genetically.