Intracellular bacterial symbiosis in the genus Sitophilus: the 'biologicalindividual' concept revisited

Eukaryotic cells, as genetic entities, most often involve several physicall y associated genomes that direct the metabolic cell equilibrium. In the col eopteran insects of the genus Sitophilus, in addition to the nucleus and th e mitochondrial genomes, two other intracellular bacterial genomes belongin g to the alpha and the gamma groups of Proteobacteria are also present. Coe xisting with the eukaryotic host cell genomes, they intervene in the physio logy and reproduction of the host. They are both transmitted vertically to the progeny and exhibit different levels of symbiont integration in insects . Their coexistence within a eukaryotic cell system illustrates the genetic complexity of animal tissue and questions the concept of the 'biological i ndividual', (C) 2001 Editions scientifiques et medicales Elsevier SAS.