Bioluminescence of myctophid and stomiiform fishes is not due to bacterial luciferase

Abstract

AbstractA recent report by D. Foran proposes that bioluminescence of myctophids and some stomiiform fishes is due to bacterial symbionts in their photophores, based on positive hybridization of bacterial luminescence (lux) gene probes to DNA from muscle and skin of myctophids and stomiiforms and in situ hybridization. Previous microscopic studies have not revealed the presence of bacteria in these fishes, and bioluminescence of myctophids has been attributed to a coelenterazine‐based system. We have investigated this finding by assay of bacterial luciferase and by lux hybridization to DNA from photophores and control samples in order to determine whether bacterial symbionts or bacterial lux genes are present in these fishes. Results of enzyme assays of photophores from six species of myctophids and two species of stomiiforms show bacterial luciferase activity ranging from 0 to 7 × 105 quanta sec−1 mg wet weight−1. The highest levels detected were 3–4 orders of magnitude less than the activity of luminous bacteria and symbiotic light organ extracts, and were less than or equal to the activity of gut homogenates, which were up to tenfold higher than the highest photophore activities. Hybridization with lux probes did not detect lux sequences in photophore DNA from three species of myctophids and three species of stomiiforms. We find no evidence that bacterial luciferase is the source of luminescence in myctophid and stomiiform light organs.