Biosynthesis and stereochemistry of the autoinducer controlling luminescence in Vibrio harveyi

Knowledge of the pathway for synthesis of the autoinducer, N-(beta-hydroxybutyryl)-homoserine lactone (HBHL), controlling luminescence in Vibrio harveyi can provide important information concerning the relationship between the nutrition and physiology of the bacteria and the phenomenon of light emission. In this study, the D and L isomers of the autoinducer containing the stereoisomers of beta-hydroxybutyric acid were synthesized and characterized by proton nuclear magnetic resonance in the presence of a chiral shift reagent, a europium(III) derivative of Tris3-(heptafluoropropyl-hydroxymethylene)-(+)-camphorato. By using a newly isolated autoinducer mutant which responds to low physiological concentrations of the autoinducer, it could be shown that autoinducer activity was associated with D-HBHL and not L-HBHL. Blockage of fatty acid biosynthesis by the addition of fatty acids and/or the antibiotic cerulenin to the cells prevented synthesis of the autoinducer as measured by the loss of autoinducer activity and a decrease in the incorporation of labelled acetate into the partially purified autoinducer. These results indicate that fatty acid biosynthesis is necessary for light emission in luminescent bacteria because it controls formation of the lux autoinducer.