Cryptic luminescence in the cold-water fish pathogen Vibrio salmonicida

The recent discovery that the fish pathogen Vibrio salmonicida is closely r elated 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 a utoinducer N-(3-oxo-hexanoyl)-L-homoserine lactone, a transcriptional activ ator of the luminescence (lux) genes. An extract of spent medium of V. salm onicida that should contain any V. salmonicida acyl-homoserine lactone auto inducer, when added to V. fischeri cells, led to an induction of their lumi nescence. These results show that V. salmonicida is a newly recognized lumi nous bacterial species that apparently both produces an autoinducer activit y and responds to exogenous V. fischeri autoinducer.