Vibrio azureus emits blue-shifted light via an accessory blue fluorescent protein

Abstract

Luminous marine bacteria usually emit bluish-green light with a peak emission wavelength (λ(max) ) at about 490nm. Some species belonging to the genus Photobacterium are exceptions, producing an accessory blue fluorescent protein (lumazine protein: LumP) that causes a blue shift, from λ(max) ≈490 to λ(max) ≈476nm. However, the incidence of blue-shifted light emission or the presence of accessory fluorescent proteins in bacteria of the genus Vibrio has never been reported. From our spectral analysis of light emitted by 16 luminous strains of the genus Vibrio, it was revealed that most strains of Vibrio azureus emit a blue-shifted light with a peak at approximately 472nm, whereas other Vibrio strains emit light with a peak at around 482nm. 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.