Luminescence-specific synthesis of myristic acid in the bioluminescent bacterium Vibrio harveyi

Abstract

The effect of bioluminescence development on the metabolism of fatty acids, in particular myristic acid (14:0), which is required to form the aldehyde substrate of luciferase, has been investigated in the luminescent marine bacterium Vibrio harveyi. The induction of luminescence in late exponential growth was not accompanied by substantial changes in the fatty acid composition. However, pulse-label studies revealed a small but significant increase in the ratio of labeled 14:0 to 16:0 (palmitic acid) when induced cells were incubated with [1-14C]acetate in growth medium. Evidence consistent with a decrease in the specific radioactivity of the acetate precursor in actively luminescing cells was also obtained. No free 14C-labeled fatty acid or aldehyde was detected under normal growth conditions. In contrast, unesterified [14C]14:0 (up to 15% of the total lipid label) transiently accumulated when wild type cells were labeled with [1-14C]acetate in a nutrient-free medium. No preferential synthesis of 14:0 or free fatty acid was detected under any conditions in preinduced cells or in a dark mutant of V. harveyi (mutant M17), which is defective in a luminescence-related acyltransferase and is thus incapable of providing fatty acid for light emission. Combined with previous evidence indicating that this acyltransferase can catalyze the deacylation of fatty acyl-acyl carrier protein (acyl-ACP) in vitro, the present results support a model in which 14:0 is diverted from phospholipid synthesis to the luminescence system at the level of 14:0-ACP. Under normal growth conditions, the requirement of 14:0-ACP via this pathway does not appear to substantially alter the overall fatty acid composition during the development of bioluminescence.