The yellow bioluminescence bacterium, Vibrio fischeri Y1, contains a bioluminescence active riboflavin protein in addition to the yellow fluorescence FMN protein.

The yellow bioluminescence Y1 strain of Vibrio fischeri can produce a 22 kDa protein with either FMN or riboflavin as a bound fluorophore. Both forms are active for shifting the bioluminescence spectral maximum. The fluorescence spectral distribution of the two proteins differs slightly and the in vivo emission appears to be an equal mixture of the two. The bioluminescence activity of the riboflavin Y1 protein contrasts with the inactivity of the related Photobacterium type.