409 Aerobic to anaerobic transition in the carbohydrate metabolism of Schistosoma mansoni cercariae during transformation in vitro B. E. P. VAN OORDT, A. G. M. TIELENS* and S. G. VAN DEN BERGH Laboratory of Veterinary Biochemistry, Utrecht University, P.O. Box 80.176, 3508 TD Utrecht, The Netherlands (Accepted 12 November 1988) SU M M ARY 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 carbo- hydrate 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 pymvate 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. Key words: Schisotoma mansoni, carbohydrate metabolism, cercariae, metabolic transition. INTRODUCTION Many alterations in the structure and physiology of Schistosoma mansoni accompany the transformation of a cercaria into a schistosomulum (Stirewalt, 1974). One of the most notable changes is the transition of an aerobic to a more anaerobic energy metabolism (Von Kruger et al. 1978; Thompson et al. 1984). Remarkably, our knowledge of this metabolic tran- sition - the external or internal factors it is influenced by, its relationship to other transformational changes, or the exact moment in the developmental cycle it takes place — is far from complete. At the moment, the general opinion (Coles, 1984) is that loss of the cercarial tail causes the transition from an aerobic metabolism to the production of lactate in aerobic conditions (Von Kruger et al. 1978), whereas Krebs-cycle activity is minimized within several hours after tail loss (Thompson et al. 1984). Other data from the literature, however, suggest that various external factors may be of importance in bringing about the transition. These include: (1) an increase in temperature to 37 °C; an increase from 27 to 37 °C has been reported to induce rapid per- meability changes in cercariae and schistosomula (Ramalho-Pinto et al. 1975); these permeability changes may be associated with a transition in metabolism; (2) changes in pH, since pH is im- portant in determining the rate of the permeability change (Ramalho-Pinto et al. 1975, 1974); (3) an increase of external glucose concentration, as may be concluded from the observed decrease in oxygen * Reprint requests to Dr A. G. M. Tielens. consumption by cercariae in water after addition of glucose (Von Kruger et al. 1978; Bruce, Ruff & Hasegawa, 1971); (4) an increase of the osmolarity of the incubation medium, since a transient lactate production has been reported when cercariae are transferred from water into a simple salt solution (Coles, 1972); moreover, biological transformation without tail loss occurs in simple salt solutions (Stirewalt, Cousin & Dorsey, 1983; Cousin et al. 1986a; Cousin, Stirewalt & Dorsey, 19866); (5) ageing of cercariae, since aged cercariae are reported to take up larger quantities of glucose than freshly- shed organisms (Bruce et al. 1969). In this paper, we present experiments on the metabolic transition. First, cercariae were incubated in water and their carbohydrate metabolism was determined. Secondly, the influence of isotonic media (280-300 mOsm) and of added glucose on freshly-shed cercariae was analysed. Thirdly, the metabolism was investigated after pre-incubation for 18 h under different transformation conditions. MATERIALS AND METHODS Chemicals Bovine serum albumin (BSA) was obtained from Boehringer (Mannheim, FRG), defatted with active carbon and dialysed before use. Foetal calf serum (FCS) and antibiotics were purchased from Flow Laboratories (Irvine, Scotland). FCS was treated for 40min at 56 °C before use. NCTC-135, for the preparation of NCTC-109, was from Serva (Heidel- berg, FRG). Other enzymes and fine chemicals came Parasilology (1989), 98, 409^15 Printed in Great Britain https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0031182000061497 Downloaded from https://www.cambridge.org/core. IP address: 54.191.40.80, on 14 Jul 2017 at 12:48:07, subject to the Cambridge Core terms of use, available at