, 1983). Modulation of the light emission spectrum is often observed among luminous organisms, such as Aequorea victoria (Shimomura et al., 1962), and has been observed in three species of luminous bacteria (Photobacterium phosphoreum, Photobacterium leiognathi, and Aliivibrio sifiae strain Y1 [formerly known as Vibrio fischeri strain Y1]). The mechanism of this phenomenon was initially characterized in P. phosphoreum strain A-13 (Gast UK-371804 cost & Lee, 1978). The maximal emission wavelength (λmax ≈ 476 nm) of this

strain is blue-shifted in comparison with that of purified luciferase (λmax ≈ 490 nm). Gast & Lee (1978) showed that this blue shift was caused by the involvement of an accessory blue fluorescent protein, of which the fluorescent spectrum was identical to the in vivo light emission spectrum. This protein was also found in P. leiognathi (O’Kane et al., 1985) and is now called lumazine protein (LumP). LumP has 6,7-dimethyl-8-(1′-d-ribityl) lumazine as its chromophore (Koka & Lee, 1979). In

another case, an accessory yellow fluorescent protein (YFP) was discovered Sirolimus price in the yellow-light-emitting V. fischeri strain Y1 (Daubner et al., 1987), which has been recently reclassified as A. sifiae (Ast et al., 2009; Yoshizawa et al., 2010b). YFP modulates the light emission wavelength of bacterial luciferase to yellow (λmax ≈ 540 nm). These proteins are involved

in the luciferase reaction, and it is generally accepted that the peak emission wavelengths of the light emission spectra are shifted to shorter or longer wavelengths that correspond to the spectra of these fluorescent proteins (Gast & Lee, 1978; Small et al., 1980; Karatani et al., 1992). There are, however, no reports of an accessory fluorescent protein in bacteria of the genus Tryptophan synthase Vibrio. The aim of this study was to explore luminous bacteria with modulated light emission in the genus Vibrio and to see whether these bacterial strains carry an accessory fluorescent protein. We performed detailed analyses of the light emission spectra and the luxA gene sequences in 16 strains of four luminous Vibrio species (Vibrio harveyi, Vibrio campbellii, Vibrio azureus, and Vibrio jasicida). Multilocus sequence analysis (MLSA) was used for bacterial identification. Furthermore, the protein involved in the shift was purified and subjected to spectral base characterization in vitro. As a result, we obtained a new fluorescent protein responsible for the blue-shifted light emission of V. azureus. We used 16 luminous strains of genus Vibrio (Table 1). Bacterial strains newly reported in this study were isolated from seawater samples from Sagami Bay (35°00′N, 139°20′E), the Pacific equatorial zone, and Aburatsubo Inlet (35°09′N, 139°36′E).