Dynamics of redox potential and changes in redox state of iron and humic acids during gut passage in soil-feeding termites (Cubitermes spp.)

The diet of soil-feeding termites contains large amounts of redox-active humic substances and inorganic compounds such as nitrate, sulfate, and iron minerals, which are potential mediators and/or electron acceptors for the mineralization of organic matter. We have shown previously that the intestinal tract of Cubitermes spp. (Isoptera, Termitidae) is characterized by strong changes in oxygen and hydrogen partial pressures and an extreme alkalinity of the anterior hindgut. Microelectrode measurements performed in this study indicated that the intestinal redox potential is controlled not only by the presence of oxygen or hydrogen and the prevailing pH in the different gut compartments, but also by other electroactive components. Speciation of the acid-extractable iron showed that parent soil and nest material contained mostly iron(III), whereas the gut contained mainly iron(II). Also, the humic acids in the individual gut compartments were more reduced than those in parent soil or feces. Together, these findings indicate that humic acid reduction and ferric iron reduction are important processes for the mineralization of soil organic matter in the gut of soil-feeding termites.