Schistosoma mansoni cercariae in water were shown to possess a largely aerobic energy metabolism, the Krebs cycle being the main terminal of carbohydrate breakdown. A metabolic transition towards a more anaerobic breakdown of carbohydrate could be achieved by incubation conditions which also stimulated biological transformation. Incubation of cercariae in a simple salt medium containing 5 mM glucose induced such a metabolic transition: beside carbon dioxide large amounts of lactate and pyruvate were excreted. The results indicate that the production of pyruvate was coupled to electron transfer in the respiratory chain. Some aspects of this unusual pyruvate production are discussed. The observed change in the end-product pattern of carbohydrate breakdown is very rapid: most of the switch occurred within 2 h. Our results show that the metabolic transition was triggered by the biological transformation itself, or by the same event that induces the biological transformation. The metabolic and the biological changes proceeded synchronously.

No abstract

A detailed study was made of the changes in the carbohydrate metabolism of Schistosoma mansoni occurring during both the penetration of the skin of a hamster and the subsequent development of the schistosome in the lung, liver, and mesenteric veins of the host. During infection, within a few hours a transition occurs from a fully aerobic to a largely anaerobic energy metabolism. By 5 h postinfection, about 6% of carbohydrate breakdown occurs in the aerobic reactions of the Krebs cycle, whereas the rest occurs in the anaerobic formation of lactate. The contribution of aerobic processes to carbohydrate breakdown remains at this level of 6% until 3 weeks postinfection and then gradually declines to the adult level of 2.5%. Measurement of the protein content of developing schistosomes shows that an exponential growth occurs over a 15-day period after the arrival of the schistosomes in the liver (days 11-25 postinfection). During this period the protein content of the parasites increases about 100-fold, but despite this change in size, no major changes occur in the end-product pattern of carbohydrate breakdown. We conclude that during this period the rate of oxygen diffusion into the tissues is not a limiting factor for aerobic metabolism. A limited diffusion of oxygen may play a role in the decreasing contribution of aerobic processes during the later stages of maturation of the schistosomes.

No abstract