(Click on the front page image to download the full article) Summary: Unicorns (Equus unicornis) are a rare terrestrial mammal, which have been noted to produce a variegated pigmented feces that is often referred to as “rainbow poop.” Despite considerable commercial interest in unicorn rainbow poop, the mechanism leading to this rainbow-pigmentation remains unknown. Microbial metabolism—including the production of pigments— can influence the perceived color of animal excreta. To determine if the rainbow pigments of unicorn feces could have a microbial origin, we used a bioinformatic and microbial cultivation-based approach. To establish what microorganisms could be producing such colored pigments,…