The termite gut microflora as an oxygen sink: microelectrode determination of oxygen and pH gradients in guts of lower and higher termites

• Published in: Applied and Environmental Microbiology 1995-07, Vol.61 (7), p.2681-2687
• Main Authors: Brune, A. (Michigan State University, East Lansing, MI.), Emerson, D, Breznak, J.A
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; APPAREIL DIGESTIF; Biochemistry; Biochemistry. Physiology. Immunology; Biological and medical sciences; CONSOMMATION D'OXYGENE; CONSUMO DE OXIGENO; Digestive system; ELECTRODE; ELECTRODOS; FLORA MICROBIANA; FLORE MICROBIENNE; Fundamental and applied biological sciences. Psychology; Insecta; Insects; INTESTIN; INTESTINOS; Invertebrates; Isoptera; Microbial ecology; NASUTITERMES; Normal microflora of man and animals. Rumen; OXIGENO; OXYGENE; Physiology. Development; RETICULITERMES FLAVIPES; Rhinotermitidae; SISTEMA DIGESTIVO; TERMITIDAE
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.61.7.2681-2687.1995

Clark-type oxygen microelectrodes and glass pH microelectrodes, each with a tip diameter of less than or equal to 10 microgram, were used to obtain high-resolution profiles of oxygen concentrations and pH values in isolated termite guts. Radial oxygen profiles showed that oxygen penetrated into the peripheral hindgut contents up to about 150 to 200 microgram below the epithelial surface in both the lower termite Reticulitermes flavipes (Kollar) and the higher termite Nasutitermes lujae (Wasmann). Only the central portions (comprising less than 40% of the total volume) of the microbe-packed, enlarged hindgut compartments ("paunches") were completely anoxic, indicating that some members of the hindgut microbiota constitute a significant oxygen sink. From the slopes of the oxygen gradients, we estimated that the entire paunches (gut tissue plus resident microbiota) of R. flavipes and N. lujae accounted for 21 and 13%, respectively, of the respiratory activity of the intact animals. Axial oxygen profiles also confirmed that in general, only the paunches were anoxic in their centers, whereas midguts and posterior hindgut regions contained significant amounts of oxygen (up to about 50 and 30% air saturation, respectively). A remarkable exception to this was the posterior portion of an anterior segment (the P1 segment) of the hindgut of N. lujae, which was completely anoxic despite its small diameter (approximately 250 microgram). Axial pH profiles of the guts of Nasutitermes nigriceps (Haldeman) and Microcerotermes parvus (Haviland) revealed that there were extreme shifts as we moved posteriorly from the midgut proper (pH approximately 7) to the P1 segment of the hindgut (pH 10) and then to the P3 segment (paunch; pH approximately 7). The latter transition occurred at the short enteric valve (P2 segment) and within a distance of less than 500 microgram. In contrast, R. flavipes, which lacks a readily distinguishable P1 segment, did not possess a markedly alkaline region