Additionally, two genes encoding channels associated with osmotic stress response (mscL and ybaL) have been preserved in its genome. The fact that this kind of molecule has not been identified in other P-endosymbionts with reduced genomes might indicate their connection with special

requirements of nested endosymbiosis, and might be involved in the exchange of molecules between both partners. On the other hand, T. princeps does not resemble any known organelle, but it would not be reasonable to consider it, in a strict sense, check details as a living organism, since it has lost many essential genes involved in informational functions, as well as most metabolic pathways except for the ability to synthesize most essential amino acids, some of which require the cooperation of M. endobia and the host [16]. T. princeps retains most, but not all, of the translation machinery, for which it also seems to depend on M. selleck compound endobia, even though almost half of its coding BI 10773 capacity is devoted to this function [16, 19]. Additionally, it is unable to replicate on its own, although one can hypothesize

that composite DNA and RNA polymerases (made of subunits encoded in both genomes) perform this function. T. princeps appears to be completely dependent on M. endobia for the synthesis of ATP, nucleotides or its cellular envelope, but still retains a complete set of molecular chaperones and proteins needed for the synthesis of [Fe-S] clusters. Another intriguing fact revealed by our analysis is the overrepresentation of tRNAs genes in the M. endobia genome. This fact, together with the duplication in the rRNA operon in both genomes, appears to indicate an important translational activity in which both endosymbionts seem to be PAK5 engaged. However, it lacks tRNA-Lys(AAG) which, surprisingly, has two functional copies in the

small genome of T. princeps. This might be an indication that there is a mutual exchange of molecules between both compartments, although further studies are required to demonstrate this. Nature is prolific in instances of symbiotic cooperation to give rise to new organisms, and new discoveries are always possible. Taking into consideration the deduced exceptional complementation inferred for this endosymbiotic system, we propose that T. princeps and M. endobia should be considered part of a new composite organism rather than a bacterial consortium. Methods Insect sample collection and DNA extraction A population of P. citri from an initial sample obtained from a Cactaceae at the Botanical Garden of the Universitat de Valencia (Valencia, Spain) was reared in the laboratory at room temperature, fed on fresh pumpkins and used for genome sequencing. Two other populations of P. citri were used for additional experiments.