Facultative Anaerobiosis in the Invertebrates: Pathways and Control Systems

Abstract

SYNOPSIS. An increasing number of the invertebrates studied have been found to rely on an anaerobic energy metabolism during at least one stage in their development. Some of the bivalve mollusks, and particularly a relatively large number of parasitic nematodes, cestodes, trematodes and acanthocephala may be classified in this category. Regardless of the aerobic or anaerobic requirements of the parasitic helminths, two features appear to be common to all members of this group which have been examined. First, they are all capable of taking up oxygen. Second, none can oxidize substrates completely to CO2 and H2O; end-products of fermentation invariably accumulate, indicating either the complete absence or the presence of only a limited terminal respiratory pathway. The intes inal nematode, Ascaris lumbricoides, has served as a model system for the elucidation of an anaerobic energy-yielding pathway of carbohydrate dissimilation which appears to beoperative in the anaerobic stages of a number of other invertebrates. This pathway differs in several major respects from those previously described for mammalian and other aerobic tissues. The Ascaris system is discussed in detail and is compared with other invertebrate and vertebrate metabolisms.