Aerobic and anaerobic metabolism in the higher termite Nasutitermes walkeri (Hill)

Abstract

An attempt has been made to interpret, in terms of energy metabolism, the rates at 25°C of O 2 consumption, 85.90±1.68 nmol/termite/h, and CO 2 production, 88.40±2.29 nmol/termite/h, in freshly collected Nasutitermes walkeri. The possible roles played by glucose, xylose, pyruvate, alanine, α-ketoglutarate and acetate, as energy sources for both the termite and its bacterial symbionts, have been studied by the measurement of enzyme activities, O 2 utilisation and 14CO 2 production from 14C-labelled substrates. In termite tissues, the key enzymes of glycolysis and the tricarboxylic acid (TCA) cycle, as well as acetyl CoA synthetase were all active but pyruvate dehydrogenase complex activity was absent. The major anaplerotic enzyme in termite tissue was malic enzyme (NADPH-dependent). In the hindgut microbiota, evidence of aerobic metabolism was provided by activity of the pyruvate dehydrogenase complex and a fully functional TCA cycle, which was confirmed by the presence of α-ketoglutarate dehydrogenase complex activity, whereas enzymic evidence for anaerobic metabolism in the hindgut microbiota was shown by pyruvate-ferredoxin oxidoreductase activity. The major bacterial anaplerotic enzyme was phosphoenolpyruvate carboxykinase. These enzyme studies were complemented by aerobic and anaerobic control incubations of degutted bodies and ruptured hindguts with 14C-labelled substrates. The rate of acetate production in ruptured hindguts incubated anaerobically was similar to that of CO 2 production in live termites incubated under N 2. Variation in pyruvate concentration had more effect on O 2 utilisation and acetate production than other substrates tested in vitro.