V ibrio azureus emits blue‐shifted light via an accessory blue fluorescent protein

Luminous marine bacteria usually emit bluish‐green light with a peak emission wavelength (λ max ) at about 490 nm. Some species belonging to the genus P hotobacterium are exceptions, producing an accessory blue fluorescent protein (lumazine protein: LumP ) that causes a blue shift, from λ max  ≈ 490 to λ max  ≈ 476 nm. However, the incidence of blue‐shifted light emission or the presence of accessory fluorescent proteins in bacteria of the genus V ibrio has never been reported. From our spectral analysis of light emitted by 16 luminous strains of the genus V ibrio , it was revealed that most strains of V ibrio azureus emit a blue‐shifted light with a peak at approximately 472 nm, whereas other V ibrio strains emit light with a peak at around 482 nm. Therefore, we investigated the mechanism underlying this blue shift in V . azureus NBRC 104587 T . Here, we describe the blue‐shifted light emission spectra and the isolation of a blue fluorescent protein. Intracellular protein analyses showed that this strain had a blue fluorescent protein (that we termed VA ‐ BFP ), the fluorescent spectrum of which was almost identical to that of the in vivo light emission spectrum of the strain. This result strongly suggested that VA ‐ BFP was responsible for the blue‐shifted light emission of V . azureus .