Preferential attachment and colonization of the keratinolytic bacterium Bacillus licheniformis on black- and white-striped feathers

Feathers serve numerous functions, from flight to interspecific and intraspecific communication. Melanin has been shown to protect feathers from microbial degradation that might, for example, hinder flight or mate attraction. Most studies have focused on the physical resistance to degradation that melanin provides. However, it has yet to be addressed whether melanin alters bacterial colonization and attachment patterns before degradation. We used the common keratinolytic bacterium Bacillus licheniformis to test for preferential attachment and colonization on feathers with black (melanized) and white (unmelanized) stripes. Using experimental inoculation of Eurasian Three-toed Woodpecker (Picoides tridactylus) feathers in vitro and scanning electron microscopy, we show that B. licheniformis preferentially colonizes white feather stripes nearly twice as often as black feather stripes. These data suggest that melanin, in addition to strengthening feathers, may inhibit colonization of keratinolytic bacteria, with possible implications regarding the mechanisms of exceptional preservation of feathers and melanin in the fossil record.