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

Abstract

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 composite living being.

Comparison of the Genome Sequences of “Candidatus Portiera aleyrodidarum” Primary Endosymbionts of the Whitefly Bemisia tabaci B and Q Biotypes

“…The "Ca. Portiera" genome assembly is a 351-kb circular molecule that is highly AT biased (73%) and larger than those of other previously reported insect primary endosymbionts such as Tremblaya from mealybugs with a 139-kb genome size (8), Hodgkinia from cicadas with a 144-kb genome size (9), and Carsonella from psyllids with a 160-kb genome size (10) but smaller than those of other primary endosymbionts such as Buchnera from aphids with a 640-kb genome size (11), Blattabacterium from cockroaches with a 630-kb genome size (12), and Wigglesworthia from tsetse flies with a 698-kb genome size (13). The median sequence coverages are 223-and 185-fold for the "Ca.…”

“Wigglesworthia morsitans” Folate (Vitamin B 9 ) Biosynthesis Contributes to Tsetse Host Fitness

“…One extreme case has been described within the mealybug, where dual symbiont species and the host have retained complementary loci that, only when integrated as a symbiotic system (i.e., a holobiont) and not as individual species, are capable of producing specific requisite nutrients (3,9). Extensive gene purging is characteristic among ancient bacterial symbionts, as they challenge the lower limits of genome size (10,11). These symbionts typically exhibit tremendous genomic stasis between strains and species, likely due to their environmental isolation, as their genomes encode only those capabilities necessary for the maintenance of the mutualism (reviewed in reference 10).…”

Symbiosis—Evolution’s Co-Author

“…In essence, this tripartite mealybug symbiosis is a holobiont mosaic that may be a model for many holobiont systems across the phyla of life. It is noteworthy that this symbiotic story indicates that pathways other than transfer of symbiont genes to a "host" nucleus, as in the case with many organelles, may be at play among holobionts, given that little evidence was found that the reduction of the genomes among the symbiotic bacteria was due to gene movement to the mealybug nuclei (Lopez-Madrigal et al 2011).…”