How diverse is the genus Wolbachia? Multiple-gene sequencing reveals a putatively new Wolbachia supergroup recovered from spider mites (Acari: Tetranychidae)

Abstract

At least 20% of all arthropods and some nematode species are infected with intracellular bacteria of the genus Wolbachia. This highly diverse genus has been subdivided into eight "supergroups" (A to H) on the basis of nucleotide sequence data. Here, we report the discovery of a new Wolbachia supergroup recovered from the spider mite species Bryobia species V (Acari: Tetranychidae), based on the sequences of three protein-coding genes (ftsZ, gltA, and groEL) and the 16S rRNA gene. Other tetranychid mites possess supergroup B Wolbachia strains. The discovery of another Wolbachia supergroup expands the known diversity of Wolbachia and emphasizes the high variability of the genus. Our data also clarify the existing supergroup structure and highlight the use of multiple gene sequences for robust phylogenetic analysis. In addition to previous reports of recombination between the arthropod-infecting supergroups A and B, we provide evidence for recombination between the nematode-infecting supergroups C and D. Robust delineation of supergroups is essential for understanding the origin and spread of this common reproductive parasite and for unraveling mechanisms of host adaptation and manipulation across a wide range of hosts.

FIG. 1.

Concatenated phylogenetic tree (ML, unrooted) based on Wolbachia sequences of three protein-coding genes (gltA, ftsZ, and groEL) (1,616 bp). Strains are characterized by the names of their host species. ML bootstrap values (top numbers, in boldface) based on 100 replicates and Bayesian posterior probabilities (bottom numbers) are depicted (only values larger than 50 are indicated). Values for recently diverged taxa within supergroups are sometimes excluded for clarity of presentation. The bar indicates a branch length of 10% likelihood distance.

FIG. 2.

Unrooted ML phylogenetic tree of Wolbachia 16S rRNA gene sequences (1,255 bp). Strains are characterized by the names of their host species. ML bootstrap values (top numbers, in boldface) based on 100 replicates and Bayesian posterior probabilities (bottom numbers) are depicted (only values larger than 50 are indicated). Values for recently diverged taxa within supergroups are sometimes excluded for clarity of presentation. The bar indicates a branch length of 1% likelihood distance.

FIG. 3.

Two cases of recombination between Wolbachia 16S rRNA gene sequences. Only polymorphic sites are shown (the position in the alignment is given on top). Sequences are named by their GenBank accession numbers, supergroups (in boldface), and host species names. Different shadings indicate possible recombinant regions (see Results). Differences and identities (dots) compared to the middle sequence are shown.

FIG. 4.

Overview of recombination between Wolbachia gltA sequences of filarial nematodes (supergroups C and D). Only polymorphic sites are shown (the position in the alignment is given on top). Sequences are named by their GenBank accession numbers, supergroups (in boldface), and host species names. Different shadings indicate the similarity of the recombinant strain in W. bancrofti to each of the other strains.