Insects combat pathogenic bacteria by producing a polymer called melanin and depositing it onto the microbe's surface. But one bacterial species has a weapon of its own — a cell-surface molecule that inhibits insects' melanin-producing enzymes.
Jon Clardy at Harvard Medical School in Boston, Massachusetts, and his team pinpointed the molecule, rhabduscin, on the surface of the bacterium Xenorhabdus nematophila. Nanomolar levels of the chemical blocked the activity of a melanin-producing enzyme from waxmoth larvae. X. nematophila that lack a rhabduscin-producing enzyme were less effective at killing the larvae than were normal bacteria.
Genes that encode enzymes involved in rhabduscin production are also found in the pathogen that causes cholera, Vibrio cholerae. A similar defence mechanism might exist in this bacterium, the authors speculate.
Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1201160109 (2012)