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

Structural colors (SC), generated by light interacting with nano-structured materials, are 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. Here, we focus on moeA, 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 compared to the wild-type. The moeA 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 moeA and polysaccharide metabolism in SC. Overall, we demonstrated that a targeted approach, modifying a single gene identified by genomics, could change the optical properties of bacteria.