The gut microenvironment of sediment-dwelling Chironomus plumosus larvae as characterised with O2, pH, and redox microsensors

We devised a set-up in which microsensors can be used for characterising the gut microenvironment of aquatic macrofauna. In a small flow cell, we measured microscale gradients through dissected guts (O-2, pH, redox potential [E-h ]), in the haemolymph (O-2), and towards the body surface (O-2) of Chironomus plumosus larvae. The gut microenvironment was compared with the chemical conditions in the lake sediment in which the animals reside and feed. When the dissected guts were incubated at the same nominal O-2 concentration as in haemolymph, the gut content was completely anoxic and had pH and E (h) values slightly lower than in the ambient sediment. When the dissected guts were artificially oxygenated, the volumetric O-2-consumption rates of the gut content were at least 10x higher than in the sediment. Using these potential O-2-consumption rates in a cylindrical diffusion-reaction model, it was predicted that diffusion of O-2 from the haemolymph to the gut could not oxygenate the gut content under in vivo conditions. Additionally, the potential O-2-consumption rates were so high that the intake of dissolved O-2 along with feeding could be ruled out to oxygenate the gut content. We conclude that microorganisms present in the gut of C. plumosus cannot exhibit an aerobic metabolism. The presented microsensor technique and the data analysis are applicable to guts of other macrofauna species with cutaneous respiration.