The bacteriophage WORiC is the active phage element in wRi of Drosophila simulans and represents a conserved class of WO phages

Abstract

BackgroundThe alphaproteobacterium Wolbachia pipientis, the most common endosymbiont in eukaryotes, is found predominantly in insects including many Drosophila species. Although Wolbachia is primarily vertically transmitted, analysis of its genome provides evidence for frequent horizontal transfer, extensive recombination and numerous mobile genetic elements. The genome sequence of Wolbachia in Drosophila simulans Riverside (wRi) is available along with the integrated bacteriophages, enabling a detailed examination of phage genes and the role of these genes in the biology of Wolbachia and its host organisms. Wolbachia is widely known for its ability to modify the reproductive patterns of insects. One particular modification, cytoplasmic incompatibility, has previously been shown to be dependent on Wolbachia density and inversely related to the titer of lytic phage. The wRi genome has four phage regions, two WORiBs, one WORiA and one WORiC.ResultsIn this study specific primers were designed to distinguish between these four prophage types in wRi, and quantitative PCR was used to measure the titer of bacteriophages in testes, ovaries, embryos and adult flies. In all tissues tested, WORiA and WORiB were not found to be present in excess of their integrated prophages; WORiC, however, was found to be present extrachromosomally. WORiC is undergoing extrachromosomal replication in wRi. The density of phage particles was found to be consistent in individual larvae in a laboratory population. The WORiC genome is organized in conserved blocks of genes and aligns most closely with other known lytic WO phages, WOVitA and WOCauB.ConclusionsThe results presented here suggest that WORiC is the lytic form of WO in D. simulans, is undergoing extrachromosomal replication in wRi, and belongs to a conserved family of phages in Wolbachia.

Wolbachia Endosymbiont of the Horn Fly (Haematobia irritans irritans ): a Supergroup A Strain with Multiple Horizontally Acquired Cytoplasmic Incompatibility Genes

“…Supergroup A members wMel, wRi, wAu, and wHa have between two and four variable WO phage regions with at least one presumed intact and other WO-like degenerated phage regions (32,(35)(36)(37). We compared the intact putative prophage region of WOIrr with the predicted WO phage regions from wMel (WOMelB) and completely sequenced WO phage region from wVitA (WOVitA), to identify the conserved region using reciprocal BLASTn analysis (37,65,80). The conserved phage regions were visualized using Easyfig (Fig.…”

Large proportion of genes in one cryptic WO prophage genome are actively and sex-specifically transcribed in a fig wasp species

“…However, how the cryptic prophage WO affects its host, Wolbachia , is poorly understood. To our knowledge, WORiA and WORiB are the only two known cryptic WO prophages confirmed by real-time qPCR to have no lytic processes, but have become trapped in the chromosome of w Ri [ 23 ]. Only three ORFs within the WORiB genome have been shown with RT–PCR to be actively transcribed and may therefore have roles in Wolbachia biology [ 20 , 30 ].…”

“…To date, several putative cryptic WO prophages have been found in the sequenced Wolbachia strains [ 21 , 22 ]. However, all of these putative cryptic WO prophages occur with at least one other complete WO prophage, carrying the complete head, baseplate, and tail gene modules that are essential for proper phage function [ 22 , 23 ]. For example, prophages WORiA and WORiB are regarded as cryptic prophages in Wolbachia w Ri, which infects D. simulans , but occur with at least one active phage, WORiC [ 23 ].…”

“…However, the expression and functions of cryptic WO prophage in Wolbachia are still poorly known. Until now, only two ank genes [ 30 ] and a putative DNA adenine methyltransferase gene ( met2 ) [ 23 ] located within the cryptic WO prophage WORiB have been reported to be actively transcribed, and may play active roles in Wolbachia biology [ 20 ]. This suggests that there is an extreme paucity of data on the active transcription of the genes of cryptic WO prophages.…”

The complexity of virus systems: the case of endosymbionts

“…2). Interestingly, Wolbachia strains that harbor a complete WO phage usually have additional WO prophages that are degenerate, transcriptionally inactive [19], and, with a few exceptions [5,20], not closely related to other prophages in the same strain [15]. …”