Abstract

We previously proposed that the function of the lux operon is to produce a halotolerant flavodoxin, FP390 or P-flavin binding protein, and not to produce light. A crucial basis of this hypothesis is that almost all species of luminous bacteria emit light in culture media containing over 2% NaCl. However, Vibrio albensis (Vibrio cholerae biovar albensis) NCIMB 41 emits light in freshwater and this appears to be in direct conflict with our hypothesis. To determine why this exceptional freshwater bioluminescence is emitted, we studied the lux operon and the regulatory system of the operon in this strain, and found that expression of the operon is regulated by a system involving a derivative of 4,5-dihydroxy 2,3-pentanedione, DPD, as an inducer, and the repressor gene for the lux operon, luxO, is damaged by deletion of two nucleotides. Furthermore, to study the effect of damage to the luxO gene, pUC18 derivatives containing the damaged and repaired luxO sequences were prepared. Cells transfected with the damaged luxO sequence emitted light like the parental strain, whereas ones transfected with the repaired one did so only sparingly. Here we show that the light emission in freshwater by this strain is not in conflict with our hypothesis.