Chemical, biological and evolutionary aspects of beetle bioluminescence

Abstract

The hypothesis that luciferases evolved from ligases that acquired oxygenase and luminogenic activities, thereby contributing to the antioxidant machinery of bioluminescent organisms, is revisited here. Larvae of click beetle Pyrearinus termitilluminans (Coleoptera: Elateridae) live under conditions close to normoxia into tunnels dug into termite mounds, whereas other elaterid larvae inhabit tunnels in decaying logs, where pO2 is ∼ 2-5%. Interestingly, the catalase and superoxide dismutase (SOD) activities in click beetle larvae were found to respond to the habitat pO2 and are significantly lower in non-luminescent elaterids. Exposure of larval P. termitilluminans larvae to hyperoxia induced SOD and catalase activities concomitantly with increments in luciferase and luciferin levels mainly in the prothorax, the brightest larval segment. Thoracic luciferase activity is 1000-fold higher than in the abdomen, while SOD activity is 2-fold higher. With larval development, an expected decline in antioxidant enzyme activities was apparently compensated by an increase in luciferase activity (2-3 fold) and in urate (40-fold), a major insect antioxidant. Finally, we found that the ligase-rich fat body of larval Tenebrio molitor, a non-luminescent beetle, contains a primal luciferase-like activity. Altogether, these data strengthen the hypothesis that various bioluminescent systems may have developed from potentially chemiluminescent metabolites and ligases that acquired a dioxygenase and luminogenic function over the course of evolution. ©ARKAT USA, Inc.