Cryptic luminescence in the cold-water fish pathogen Vibrio salmonicida

The recent discovery that the fish pathogen Vibrio salmonicida is closely related to the luminous bacteria Vibrio fischeri and Vibrio logei suggested that V. salmonicida might also be capable of bioluminescence. Interestingly, cells of V. salmonicida were found to produce light in culture, but only when exposed to either an aliphatic aldehyde and/or the major V. fischeri autoinducer N-(3-oxo-hexanoyl)-L-homoserine lactone, a transcriptional activator of the luminescence (lux) genes. An extract of spent medium of V. salmonicida that should contain any V. salmonicida acyl-homoserine lactone autoinducer, when added to V. fischeri cells, led to an induction of their luminescence. These results show that V. salmonicida is a newly recognized luminous bacterial species that apparently both produces an autoinducer activity and responds to exogenous V. fischeri autoinducer.