Mid-IR imaging as a new tool to investigate waste heat production in the nematode C. elegans

Abstract

All organisms carry out metabolic processes to produce chemical energy, but these biochemical pathways are not perfectly efficient and energetic waste is lost as heat. The interplay of heat production/retention/loss in endotherms has been well studied via thermal imaging. However, there is a striking absence of literature on the thermal output of ectotherms, especially invertebrate animals. We have developed a new thermal imaging technique to investigate waste heat production in the nematode worm <i>C. elegans</i>. No direct measurement of this metabolic waste heat has been made in <i>C. elegans </i>or any other mesoinvertebrate using IR imaging techniques. In this study, thermal IR imaging was used to examine the difference in heat output between living and dead<i> C. elegans.</i> Living and dead <i>C. elegans</i> were imaged simultaneously providing a way to directly compare the temperatures of the worms. Temperature difference was used as a marker of difference in waste heat production, not absolute temperature. A cold object was used in reflectance mode to suppress the thermal background of the imaging substrate. Several different substrates with differing thermal properties were tested to minimize thermal background. The tendency for <i>C. elegans</i> to desiccate necessitated the development of sample preparation techniques that ensured the survival of the animals during imaging. Imaging revealed that there is a clear, repeatable difference in the thermal output of living <i>C. elegans</i> compared to dead animals (whose metaobolic processes have ceased). This is exciting as it points to IR imaging as being a novel investigative tool to be applied to the study of metabolism in <i>C. elegans</i>. In the future this opens the door to screening genetic mutants with known metabolic defects, thus providing useful data for the study of genes that impact metabolism.