Four intracellular genomes direct weevil biology: Nuclear, mitochondrial, principal endosymbiont, and Wolbachia

Cell physiology in the weevil Sitophilus oryzae is coordinated by three int egrated genomes: nuclear, mitochondrial, and the "S, oryzae principal endos ymbiont" (SOPE), SOPE, a cytoplasmic bacterium (2 x 10(3) bacteria per spec ialized bacteriocyte cell and 3 x 10(6) bacteria per weevil) that belongs t o the proteobacteria gamma 3-subgroup, is present in all weevils studied. W e discovered a fourth prokaryotic genome in somatic and germ tissues of 57% of weevil strains of three species, S, oryzae, Sitophilus zeamais, and Sit ophilus granarius, distributed worldwide. We assigned this Gramnegative pro karyote to the Wolbachia group (alpha-proteobacteria), on the basis of 16S rDNA sequence and fluorescence in situ DNA-RNA hybridization (FISH), Both b acteria, SOPE and Wolbachia, were selectively eliminated by combined heat a nd antibiotic treatments. Study of bacteria involvement in this insect's ge netics and physiology revealed that SOPE, which induces the specific differ entiation of the bacteriocytes, increases mitochondrial oxidative phosphory lation through the supply of pantothenic acid and riboflavin. Elimination o f this gamma 3-proteobacterium impairs many physiological traits, By contra st, neither the presence nor the absence of Wolbachia significantly affects the weevil's physiology, Wolbachia, disseminated throughout the body cells , is in particularly high density in the germ cells, where it causes nucleo cytoplasmic incompatibility. The coexistence of two distinct types of intra cellular proteobacteria at different levels of symbiont integration in inse cts illustrates the genetic complexity of animal tissue. Furthermore, evolu tionary timing can be inferred: first nucleocytoplasm, then mitochondria, t hen SOPE, and finally Wolbachia. Symbiogenesis, the genetic integration of long-term associated members of different species, in the weevil appears to be a mechanism of speciation (with Wolbachia) and provides a means for ani mals to acquire new genes that permit better adaptation to the environment (with SORE).