Lateral transfers of insertion sequences between Wolbachia, Cardinium and Rickettsia bacterial endosymbionts

Abstract

Various bacteria live exclusively within arthropod cells and collectively act as an important driver of arthropod evolutionary ecology. Whereas rampant intra-generic DNA transfers were recently shown to have a pivotal role in the evolution of the most common of these endosymbionts, Wolbachia, the present study show that inter-generic DNA transfers also commonly take place, constituting a potent source of rapid genomic change. Bioinformatic, molecular and phylogenetic data provide evidence that a selfish genetic element, the insertion sequence ISRpe1, is widespread in the Wolbachia, Cardinium and Rickettsia endosymbionts and experiences recent (and likely ongoing) transfers over long evolutionary distances. Although many ISRpe1 copies were clearly expanding and leading to rapid endosymbiont diversification, degraded copies are also frequently found, constituting an unusual genomic fossil record suggestive of ancient ISRpe1 expansions. Overall, the present data highlight how ecological connections within the arthropod intracellular environment facilitate lateral DNA transfers between distantly related bacterial lineages.

Presence of Extensive Wolbachia Symbiont Insertions Discovered in the Genome of Its Host Glossina morsitans morsitans

“…The rearrangements in Wolbachia may have arisen from the introduction and expansion of the repeat element families that could serve as sites for intragenomic recombination, as has been shown to occur for some other bacterial species [27], [82], [83].…”

The defensive Spiroplasma

“…Despite the prevailing pattern of evolutionary mobility of RIPs and clear precedent for genetic transfer among facultative symbionts such as Wolbachia, Rickettsia, and Cardinium, e.g. ref 38 , this diversity of RIP genes appears not to have leaked to other symbiont lineages. The alternative genetic code of Spiroplasma encodes the amino acid tryptophan using the standard stop codon, UGA, making Spiroplasma genes dead-on-arrival in most recipient genomes and effectively hoarding special host phenotypes produced by RIPs within the genus 39 .…”

Phylogenomic analyses uncover origin and spread of the Wolbachia pandemic

“…Interestingly, two of the annotated genes present in all arthropod Wolbachia, but missing in supergroups C and D, are competence-related, that is, involved in uptake of external DNA (Supplementary Table 2). Exchange of genetic elements is common in Wolbachia and other endosymbionts 40 , but may be reduced like any other nonessential functions in stable obligate symbioses 41 . Similarly, phage WO genes are absent in supergroups C and D, but might have been present at some time in these groups 42 .…”