Free radicals and chemiluminescence as products of the spontaneous oxidation of sulfide in seawater, and their biological implications.

ABSTRACT

The discovery of symbioses between marine invertebrates and sulfide-oxidizing bacteria at deep-sea hydrothermal vents and in other high-sulfide marine environments has stimulated research into the adaptations of metazoans to potentially toxic concentrations of sulfide. Most of these studies have focused on a particular action of sulfide--its disruption of aerobic metabolism by the inhibition of mitochondrial respiration--and on the adaptations of sulfide-tolerant animals to avoid this toxic effect (1). We propose that sulfidic environments impose another, hitherto over-looked type of toxicity exposure to free radicals of oxygen, which may be produced during the spontaneous oxidation of sulfide, thus imposing an oxidative stress. Here we present evidence that oxygen- and sulfur-centered free radicals are produced during the oxidation of sulfide in seawater, and we propose a reaction pathway for sulfide oxidation that is consistent with our observations. We also show that chemiluminescence at visible wavelengths occurs during sulfide oxidation, providing a possible mechanism for the unexplained light emission from hydrothermal vents (2, 3).