Complete Genome Sequence of “Candidatus Tremblaya princeps” Strain PCVAL, an Intriguing Translational Machine below the Living-Cell Status

The sequence of the genome of “Candidatus Tremblaya princeps ” strain PCVAL, the primary endosymbiont of the citrus mealybug Planococcus citri, has been determined. “Ca. Tremblaya princeps ” presents an unusual nested endosymbiosis and harbors a gammaproteobacterial symbiont within its cytoplasm in all analyzed mealybugs. The genome sequence reveals that “Ca. Tremblaya princeps ” cannot be considered an independent organism but that the consortium with its gammaproteobacterial symbiotic associate represents a new com-posite living being. Obligate intracellular bacteria are characterized by their ge-nome reduction due to the loss of genes rendered unnecessary in their protected environments. However, they are still able to fulfill the essential cellular functions that allow them to repli-cate and synthesize their own proteins (7). Mealybugs contain a primary (P) endosymbiont, “Candidatus Tremblaya prin-ceps, ” which harbors a secondary (S) symbiont in its cytoplasm; this is the first described case of a nested bacterial symbiosis (10, 12)