Using deuterium as an isotopic tracer to study the energy metabolism of infective juveniles of Steinernema carpocapsae under aerobic conditions

Changes in survival, mean dry weight, levels of key energy reserve compound s and respiration of non-feeding infective juveniles (IJs) of Steinernema c arpocapsae, incubated in various ratios of D2O/H2O on a shaker at 28 degree sC were determined. Patterns of deuterium distribution in trehalose, glycog en and key fatty acids of the IJs incubated in 50% (v/v) D2O/H2O were also examined. The rates of decline in mean dry weight and lipid levels of IJs i ncubated in D2O/H2O were propaltional, while the survival times of IJs were inversely proportional, to the ratio of D2O/H2O. Deuterium was randomly an d extensively incorporated into the C-H bonds of trehalose and glycogen but was barely incorporated in fatty acid moieties of the IJs. The changes in the patterns and the extents of deuterium incorporation, as well as the lev els of trehalose, glycogens and fatty acids during the experimental period indicate that: (1) The lipogenesis pathway is not functioning in the Ijs. ( 2) Trehalose and glycogen are constantly consumed and replenished and they are mainly derived from lipids. (3) Futile cycles involving trehalose and g lycogen, which enable IJs to regulate the levels of these two compounds mor e effectively, may exist. The results support the view that lipids are the primary energy reserve of the IJs while trehalose, glycogen and proteins ca n be used for energy generation, even though this is not their primary role . (C) 2000 Elsevier Science Inc. All rights reserved.