Abstract
Research interest in Wolbachia is growing as new discoveries and technical advancements reveal the public health importance of both naturally occurring and artificial infections. Improved understanding of the Wolbachia bacteriophages (WOs) WOcauB2 and WOcauB3 [belonging to a sub-group of four WOs encoding serine recombinases group 1 (sr1WOs)], has enhanced the prospect of novel tools for the genetic manipulation of Wolbachia. The basic biology of sr1WOs, including host range and mode of genomic integration is, however, still poorly understood. Very few sr1WOs have been described, with two such elements putatively resulting from integrations at the same Wolbachia genome loci, about 2 kb downstream from the FtsZ cell-division gene. Here, we characterize the DNA sequence flanking the FtsZ gene of wDam, a genetically distinct line of Wolbachia isolated from the West African onchocerciasis vector Simulium squamosum E. Using Roche 454 shot-gun and Sanger sequencing, we have resolved >32 kb of WO prophage sequence into three contigs representing three distinct prophage elements. Spanning ≥36 distinct WO open reading frame gene sequences, these prophage elements correspond roughly to three different WO modules: a serine recombinase and replication module (sr1RRM), a head and base-plate module and a tail module. The sr1RRM module contains replication genes and a Holliday junction recombinase and is unique to the sr1 group WOs. In the extreme terminal of the tail module there is a SpvB protein homolog—believed to have insecticidal properties and proposed to have a role in how Wolbachia parasitize their insect hosts. We propose that these wDam prophage modules all derive from a single WO genome, which we have named here sr1WOdamA1. The best-match database sequence for all of our sr1WOdamA1-predicted gene sequences was annotated as of Wolbachia or Wolbachia phage sourced from an arthropod. Clear evidence of exchange between sr1WOdamA1 and other Wolbachia WO phage sequences was also detected. These findings provide insights into how Wolbachia could affect a medically important vector of onchocerciasis, with potential implications for future control methods, as well as supporting the hypothesis that Wolbachia phages do not follow the standard model of phage evolution.
Highlights
It is estimated that Wolbachia naturally infect about 40% of arthropods, including many important disease vectors (Bourtzis et al, 2014; Zug and Hammerstein, 2015)
The 11 gene sequences occur in the same order and orientation as in WOcauB2, representing the conserved group 1 serine recombinase and replication module which is unique to and highly conserved among, the sr1WO group bacteriophages (Figure 2 and below)
In this study we have shown that the genome of a geneticallydistinct Wolbachia named here as wDam harbors at least one serine recombinase Wolbachia prophage relic
Summary
It is estimated that Wolbachia naturally infect about 40% of arthropods, including many important disease vectors (Bourtzis et al, 2014; Zug and Hammerstein, 2015). Despite the potential of WO-based tools and the growing interest in the use of Wolbachia for vector-borne disease control, there are presently no genetic manipulation tools available for the genetic engineering of Wolbachia (LePage and Bordenstein, 2013; Bourtzis et al, 2014; Slatko et al, 2014; Hoffmann et al, 2015; Jeffries and Walker, 2015). There is, a growing need for a better understanding of the basic biology, diversity and distribution of naturally occurring WOs to assess the feasibility and potential utility of WO-based Wolbachia manipulation tools (Tanaka et al, 2009; LePage and Bordenstein, 2013; Wang et al, 2013). There is a pressing need to improve our understanding about how naturally
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