Abstract
The obligate intracellular bacterium, Wolbachia pipientis (Rickettsiales), is a widespread, vertically transmitted endosymbiont of filarial nematodes and arthropods. In insects, Wolbachia modifies reproduction, and in mosquitoes, infection interferes with replication of arboviruses, bacteria and plasmodia. Development of Wolbachia as a tool to control pest insects will be facilitated by an understanding of molecular events that underlie genetic exchange between Wolbachia strains. Here, we used nucleotide sequence, transcriptional and proteomic analyses to evaluate expression levels and establish the mosaic nature of genes flanking the T4SS virB8-D4 operon from wStr, a supergroup B-strain from a planthopper (Hemiptera) that maintains a robust, persistent infection in an Aedes albopictus mosquito cell line. Based on protein abundance, ribA, which contains promoter elements at the 5′-end of the operon, is weakly expressed. The 3′-end of the operon encodes an intact wspB, which encodes an outer membrane protein and is co-transcribed with the vir genes. WspB and vir proteins are expressed at similar, above average abundance levels. In wStr, both ribA and wspB are mosaics of conserved sequence motifs from Wolbachia supergroup A- and B-strains, and wspB is nearly identical to its homolog from wCobU4-2, an A-strain from weevils (Coleoptera). We describe conserved repeated sequence elements that map within or near pseudogene lesions and transitions between A- and B-strain motifs. These studies contribute to ongoing efforts to explore interactions between Wolbachia and its host cell in an in vitro system.Electronic supplementary materialThe online version of this article (doi:10.1007/s00203-015-1154-8) contains supplementary material, which is available to authorized users.
Highlights
Wolbachia pipientis (Rickettsiales; Alphaproteobacteria) is an obligate intracellular bacterium that infects filarial nematodes and a wide range of arthropods including ≥60 % of insects and ≈35 % of isopod crustaceans, but does not infect vertebrates (Hilgenboecker et al 2008)
The status of Wolbachia as a species remains unclear (Baldo et al 2006b; Lo et al 2007), a notable distinction between WOL-C-/D-strains that associate with nematodes as mutualists and WOL-A-/B-strains that occur as reproductive parasites in insects relates to genome stability and phylogenetic congruence between Wolbachia and its host
Wolbachia appears to engage in frequent horizontal gene transfer, resulting in a lack of phylogenetic congruence manifested by gene structures that represent mosaic recombinations from genomes considered distinct strains
Summary
Wolbachia pipientis (Rickettsiales; Alphaproteobacteria) is an obligate intracellular bacterium that infects filarial nematodes and a wide range of arthropods including ≥60 % of insects and ≈35 % of isopod crustaceans, but does not infect vertebrates (Hilgenboecker et al 2008). Arthropod-associated A- and B-strains may provide subtle fitness benefits to hosts (Zug and Hammerstein 2014), they are best known as reproductive parasites, causing phenotypes that maintain or increase Wolbachia infection frequencies, including. T4SS effector proteins that manipulate host cells have been identified from Anaplasma and Ehrlichia (Liu et al 2012; Lockwood et al 2011; Niu et al 2010), and Wolbachia express both vir operons in ovaries of arthropod hosts, wherein T4SS effectors are suspected to play a role in cytoplasmic incompatibility and other reproductive distortions (Masui et al 2000; Rances et al 2008; Wu et al 2004). We discuss implications for functional integration of the Wolbachia T4SS with WspB and with the riboflavin biosynthesis pathway enzymes GTP cyclohydrolase II (RibA) and dihydroxybutanone phosphate synthase (RibB)
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