Abstract
SummaryThere is increasing interest in the heritable bacteria of invertebrate vectors of disease as they present novel targets for control initiatives. Previous studies on biting midges (Culicoides spp.), known to transmit several RNA viruses of veterinary importance, have revealed infections with the endosymbiotic bacteria, Wolbachia and Cardinium. However, rickettsial symbionts in these vectors are underexplored. Here, we present the genome of a previously uncharacterized Rickettsia endosymbiont from Culicoides newsteadi (RiCNE). This genome presents unique features potentially associated with host invasion and adaptation, including genes for the complete non‐oxidative phase of the pentose phosphate pathway, and others predicted to mediate lipopolysaccharides and cell wall modification. Screening of 414 Culicoides individuals from 29 Palearctic or Afrotropical species revealed that Rickettsia represent a widespread but previously overlooked association, reaching high frequencies in midge populations and present in 38% of the species tested. Sequence typing clusters the Rickettsia within the Torix group of the genus, a group known to infect several aquatic and hematophagous taxa. FISH analysis indicated the presence of Rickettsia bacteria in ovary tissue, indicating their maternal inheritance. Given the importance of biting midges as vectors, a key area of future research is to establish the impact of this endosymbiont on vector competence.
Highlights
Heritable bacteria represent an important component of the biology of many arthropods
Culicoides newsteadi N5 is morphologically and genetically similar to C. punctatus, which has been previously reported to be infected with Cardinium symbiotic bacteria (Lewis et al, 2014)
During a shallow illumina whole genome sequencing of C. newsteadi N5, we identified the presence of several contigs with homology to Rickettsia bacteria (Supporting Information Fig. S1)
Summary
Heritable bacteria represent an important component of the biology of many arthropods. Carried by over half of all species (Weinert et al, 2015), many vertically transmitted microbes contribute to host function. This contribution is most commonly through specific services, such as nutrient provisioning or protection (Oliver et al, 2003; Douglas, 2009; Jaenike et al, 2010). Their maternalinheritance has led symbionts to favour production of daughters by their host, leading to the evolution of systems biasing offspring sex ratio towards females (reproductive parasitisms) (Hurst and Frost, 2015). This study has the complementary motivations of understanding the dynamics and ecological impact of symbionts (Ferrari and Vavre, 2011) and applying this knowledge to modify the biological properties of target species (Iturbe-Ormaetxe et al, 2011)
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