Biochemistry of milky disease: Radiorespirometry of pyruvate, acetate, succinate, and glutamate oxidation by healthy and diseased Japanese beetle larvae

Abstract

Oxidation of pyruvate, acetate, succinate, and glutamate was compared in healthy third-instar Japanese beetle ( Popillia japonica) larvae and in those infected with the milky disease bacterium, Bacillus popilliae. Both healthy and infected larvae oxidize these compounds via the tricarboxylic acid cycle. However, oxidation of all compounds, except succinate, is higher in healthy than in infected larvae. The oxidation rate of all four compounds varies throughout the infectious process. As the disease progresses, oxidation of pyruvate and glutamate is greatest in phase I when there are few observable bacterial cells within the larval hemolymph. Oxidation of acetate and succinate increases in phase II, characterized by rapid vegetative growth of the bacteria. The oxidation rate of acetate and succinate decreases upon further disease development (phases III and IV), when there is a greater demand for energy compounds and for biosynthetic intermediates by the bacterial cells in transition from vegetative growth to sporulation.