The aerobic energy metabolism of Schistosoma mansoni miracidia

Abstract

It is generally assumed that the parasitic stages of trematodes possess a predominantly anaerobic energy metabolism, excreting products of a partial degradation of glucose. On the other hand, the freeliving stages of trematodes are supposed to have an aerobic energy metabolism, relying mainly on Krebs-cycle activity for the generation of ATP [ 16]. It should be noted, however, that metabolic studies have been confined almost exclusively to the parasitic stages in the final vertebrate hosts and to the free-living stages immediately preceding them, the cercariae. Knowledge of the metabolism of the parasitic stages in the intermediate hosts and of the free-living miracidia is very limited [ 1-4]. For schistosomes it has been shown that a metabolic transition occurs when the aerobically functioning, free-living cercaria transforms into a schistosomulum, the juvenile parasitic stage in the vertebrate host, which produces mainly lactate but also relies on Krebs-cycle activity for the production of energy [7-9]. Virtually nothing is known of the metabolism of other stages in the life cycle of schistosomes. Oxygen consumption by miracidia has been observed, but its nature has not yet been investigated [ 10]. If, however, miracidia indeed have an aerobic energy metabolism whereas the parasitic stages in snails have an anaerobic one, then a second aerobic to anaerobic transition occurs in the