Effect of endocytobiotic bacteria on mitochondrial enzymatic activities in the weevil Sitophilus oryzae (Coleoptera : Curculionidae)

Abstract

Various mitochondrial enzymatic activities were investigated in symbiotic and aposymbiotic larvae and adults of Sitophilus oryzae. Six enzymes were assayed: cytochrome c oxidase, succinate cytochrome c reductase, glycerol-3-phosphate cytochrome c reductase, isocitrate dehydrogenase, pyruvate dehygrogenase, and α-ketoglutarate dehydrogenase. The specific activities of all these enzymes were higher in mitochondria isolated from symbiotic larvae than those isolated from aposymbiotic larvae. In adults, the differences in enzymatic activities between symbiotic and aposymbiotic insects were attenuated. α-Ketoglutarate dehydrogenase activity was similar in the two strains, and pyruvate dehydrogenase activity was higher in aposymbiotic strain. From the results of crosses and backcrosses between symbiotic and aposymbiotic insects we concluded that the presence of bacteria is responsible for the higher enzymatic activities in mitochondria. It is suggested that some mitochondrial metabolites could be implicated. These six enzymatic activities were also tested on symbiotic bacteria isolated from larval bacteriome. No activity was observed.