Detection of Low-Level Cardinium and Wolbachia Infections in Culicoides

Abstract

bBacterial endosymbionts have been identified as potentially useful biological control agents for a range of invertebrate vectors of disease. Previous studies of Culicoides (Diptera: Ceratopogonidae) species using conventional PCR assays have provided evidence of Wolbachia (1/33) and Cardinium (8/33) infections. Here, we screened 20 species of Culicoides for Wolbachia and Cardinium, utilizing a combination of conventional PCR and more sensitive quantitative PCR (qPCR) assays. Low levels of Cardinium DNA were detected in females of all but one of the Culicoides species screened, and low levels of Wolbachia were detected in females of 9 of the 20 Culicoides species. Sequence analysis based on partial 16S rRNA gene and gyrB sequences identified "Candidatus Cardinium hertigii" from group C, which has previously been identified in Culicoides from Japan, Israel, and the United Kingdom. Wolbachia strains detected in this study showed 98 to 99% sequence identity to Wolbachia previously detected from Culicoides based on the 16S rRNA gene, whereas a strain with a novel wsp sequence was identified in Culicoides narrabeenensis. Cardinium isolates grouped to geographical regions independent of the host Culicoides species, suggesting possible geographical barriers to Cardinium movement. Screening also identified Asaia bacteria in Culicoides. These findings point to a diversity of low-level endosymbiont infections in Culicoides, providing candidates for further characterization and highlighting the widespread occurrence of these endosymbionts in this insect group.

Torix group Rickettsia are widespread in Culicoides biting midges (Diptera: Ceratopogonidae), reach high frequency and carry unique genomic features

“…Our second finding was that Torix group Rickettsia was found commonly across biting midges. Previous work on Culicoides , using conventional PCR to establish the presence of the heritable symbiont Cardinium , revealed interspecies infection rates ranging from 16% to 29% (Nakamura et al ., ; Lewis et al ., ; Mee et al ., ). Thus, our PCR screen suggests that Rickettsia is the most common known symbiont of Culicoides , being present in 11 of 29 species tested (38%) and in 100% of specimens examined in 9 of the Rickettsia positive species.…”

“…A peculiarity of note is the detection of coexisting infected and uninfected individuals in C. impunctatus populations, a scenario contrary to the more common fixed infections observed in this study. However, low titre infections cannot be ruled out (Mee et al, 2015). Alternative explanations for this difference are that the strain in C. impunctatus has a different role in its host in comparison to the other isolates at fixation in midges.…”

“…In South America, Culicoides midges spread Oropouche virus to humans. Previous studies of Culicoides symbionts have screened extensively for Cardinium and Wolbachia infections (Nakamura et al, 2009;Morag et al, 2012;Lewis et al, 2014;Mee et al, 2015) but failed to report presence of Rickettsia. However, a 16S metagenomic screening project in Culicoides sonorensis gut samples revealed amplicons allied to Rickettsia (Campbell et al, 2004), albeit with no phylogenetic or population-based information.…”

Bluetongue: control, surveillance and safe movement of animals

“…() in Culicoides paraflavescens in Japan and in Culicoides wadai , C. brevitarsis and C. imicola in Australia by Mee et al. (). Up to date, Wolbachia has not been detected in European Culicoides species, alternatively, the genus Cardinium was detected in C. punctatus and C. pulicaris in the UK (Lewis et al., ).…”

“…Heritable bacteria cause changes in host longevity, virushost interaction and reproduction compatibility that may lead to control insect populations. Detection of endosymbiotic bacteria in biting midges has been reported by Nakamura et al (2009) in Culicoides paraflavescens in Japan and in Culicoides wadai, C. brevitarsis and C. imicola in Australia by Mee et al (2015). Up to date, Wolbachia has not been detected in European Culicoides species, alternatively, the genus Cardinium was detected in C. punctatus and C. pulicaris in the UK (Lewis et al, 2014).…”