The uropygial glands of hoopoe birds contain a symbiotic bacteria that secrete antiseptics targeted at feather-eating bacteria.

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Bacteria that consume the keratin of bird feathers are obvious enemies of birds. Without their plumage, they could not fly and would not be able to regulate their internal temperatures. The hoopoe bird prevents growth of these keratin-consuming bacteria by cultivating populations of symbiotic bacteria within special glands accessed during preening. These bacterial allies secrete antiseptics called bacteriocins that can kill the keratin-consuming bacteria. However, it appears that the birds apply enough of the antiseptic to slow the pace of keratin degradation rather than totally wiping out the bacterial parasites perhaps in an effort to ward off an aquired resistance.

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"Among potential agents that might damage bird feathers are certain microorganisms which secrete enzymes that digest keratin, as is the case of the ubiquitous bacterium Bacillus licheniformis, present in both the feathers and skin of wild birds. It is therefore a good candidate for testing the effects of bird defences against feather-degrading microorganisms. One of these defences is the oil secreted by the uropygial gland, which birds use to protect their feathers against parasites. In previous studies we have shown how Enterococcus faecalis strains isolated from nestling hoopoes exert antagonistic effects against B. licheniformis, mediated by the production of bacteriocins...These results suggest that by preening their feathers hoopoes benefit from their symbiotic relationship with bacteriocin-producing enterococci, which constitute a chemical defence against feather degradation...the bacterium E. faecalis MRR10-3, found in the uropygial gland secretion of a nestling hoopoe, produces at least two different bacteriocins with broad antimicrobial activity, including one active against B. licheniformis." (Ruiz-Rodríguez et al. 2009:3621)

"We found that both feathers and pure keratin were degraded by B. licheniformis at a much slower rate when the symbiotic bacterium E. faecalis or its bacteriocin was brought into contact...the enterococcus partially prevents the degradation of keratin by B. licheniformis and that it is completely inhibited by the isolated bacteriocin." (Ruiz-Rodríguez et al. 2009:3625)

Journal article
Symbiotic bacteria living in the hoopoe's uropygial gland prevent feather degradationJournal of Experimental BiologyOctober 30, 2009
M. Ruiz-Rodriguez, E. Valdivia, J. J. Soler, M. Martin-Vivaldi, A. M. Martin-Platero, M. Martinez-Bueno

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