The evolution of bioluminescent oxygen consumption as an ancient oxygen detoxification mechanism

Endogenous reductants such as hydrogen sulfide and alkylthiols provided fre e radical scavenging systems during the early evolution of life. The develo pment of oxygenic photosynthesis spectacularly increased oxygen levels, and ancient life forms were obliged to develop additional antioxidative system s. We develop here the hypothesis of how "prototypical" bioluminescent reac tions had a plausible role as an ancient defense against oxygen toxicity th rough their "futile" consumption of oxygen. As oxygen concentrations increa sed. sufficient light would have been emitted from such systems for detecti on by primitive photosensors, and evolutionary pressures could then act upo n the light emitting characteristics of such systems independently of their use as Futile consumers of oxygen. Finally, an example of survival of this ancient mechanism in present-day bioluminescent bacteria (in the Euprymna scolopes-Vibrio fischeri mutualism) is discussed. Once increasing ambient o xygen levels reached sufficiently high levels, the use of "futile" oxygen c onsumption became too bioenergetically costly, so that from this time the e volution of bioluminescence via this role was made impossible, and other me chanisms must be developed to account for the evolution of bioluminescence by a wide range of organisms that patently occurred after this (e.g., by in sects).