Abstract
BackgroundCardinium is an intracellular bacterial symbiont in the phylum Bacteroidetes that is found in many different species of arthropods and some nematodes. This symbiont is known to be able to induce three reproductive manipulation phenotypes, including cytoplasmic incompatibility. Placing individual strains of Cardinium within a larger evolutionary context has been challenging because only two, relatively slowly evolving genes, 16S rRNA gene and Gyrase B, have been used to generate phylogenetic trees, and consequently, the relationship of different strains has been elucidated in only its roughest form.ResultsWe developed a Multi Locus Sequence Typing (MLST) system that provides researchers with three new genes in addition to Gyrase B for inferring phylogenies and delineating Cardinium strains. From our Cardinium phylogeny, we confirmed the presence of a new group D, a Cardinium clade that resides in the arachnid order harvestmen (Opiliones). Many Cardinium clades appear to display a high degree of host affinity, while some show evidence of host shifts to phylogenetically distant hosts, likely associated with ecological opportunity. Like the unrelated reproductive manipulator Wolbachia, the Cardinium phylogeny also shows no clear phylogenetic signal associated with particular reproductive manipulations.ConclusionsThe Cardinium phylogeny shows evidence of diversification within particular host lineages, and also of host shifts among trophic levels within parasitoid-host communities. Like Wolbachia, the relatedness of Cardinium strains does not necessarily predict their reproductive phenotypes. Lastly, the genetic tools proposed in this study may help future authors to characterize new strains and add to our understanding of Cardinium evolution.
Highlights
Cardinium is an intracellular bacterial symbiont in the phylum Bacteroidetes that is found in many different species of arthropods and some nematodes
Multi Locus Sequence Typing (MLST) primers Most of the arthropod Cardinium in our set of host taxa (Table 1) could be amplified by the MLST primers (Table 2), including members from groups A, C, and D (Opiliones group)
The elongation factor G (EF-G) primers worked on all samples, the SufB and GyrB primers worked on most samples in group A and all in group C and E
Summary
Cardinium is an intracellular bacterial symbiont in the phylum Bacteroidetes that is found in many different species of arthropods and some nematodes. Even the best-known secondary symbiont, Wolbachia, a notorious host switcher, contains a clade of symbionts that display congruent evolution and co-cladogensis in their obligatory symbiosis with nematodes [11, 12] as well as a lineage that is required for B-vitamin production in bedbugs [13]. These patterns show that different strains within one group of secondary symbionts can differ dramatically in their relationships with their hosts
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