Transgenic bioluminescent C. elegans as biosensors of environmental stress

Sublethal levels of environmental stress cause temporary decreases in the ATP levels of an organism (Corton et. al., 1994). This is an early manifestation of stress that precedes effects at other levels such as development, growth, fecundity or lethality, more commonly exploited as indicators of toxicity. The change in ATP levels offers a sensitive measurement of the impact of stress and also of recovery from stress. We have generated transgenic C. elegans that express an enzyme widely used for in vitro ATP determination, firefly luciferase. The nematodes express the enzyme constitutively throughout development and emit light when provided with luciferin, the substrate for the firefly luciferase. Whole animal luminescence reflects its intracellular ATP levels in vivo. This was tested by exposing the transgenic nematodes to sodium azide. Sodium azide is a mitochondrial inhibitor and depletes ATP levels reversibly. Bioluminescence decreased with exposure to azide and recovered after worms were washed from azide in agreement with expected changes in ATP levels. Thus, this strain allows for high-throughput real-time quantification of changes in the nematode’s metabolic state resulting from stress. This is conceptually different from other available transgenic nematodes biosensors that rely on the induction of specific promoters involved in stress responses, such as the heat-shock or metallothionein promoters. We will discuss the potential of bioluminescent nematodes for environmental monitoring.

Corton et al. (1994) Current Biology 4 (4): 315-324.