Metagenomics of culture isolates and insect tissue illuminate the evolution of Wolbachia, Rickettsia and Bartonella symbionts in Ctenocephalides spp. fleas

Abstract

While fleas are often perceived simply as a biting nuisance and a cause of allergic dermatitis, they represent important disease vectors worldwide, especially for bacterial zoonoses such as plague (transmitted by rodent fleas) and some of the rickettsioses and bartonelloses. The cosmopolitan cat (Ctenocephalides felis) and dog (Ctenocephalides canis) fleas, as well as Ctenocephalides orientis (restricted to tropical and subtropical Asia), breed in human dwellings and are vectors of cat-scratch fever (caused by Bartonella spp.) and Rickettsia spp., including Rickettsia felis (agent of flea-borne spotted fever) and Rickettsia asembonensis , a suspected pathogen. These Rickettsia spp. are members of a phylogenetic clade known as the ‘transitional group’, which includes both human pathogens and arthropod-specific endosymbionts. The relatively depauperate flea microbiome can also contain other endosymbionts, including a diverse range of Wolbachia strains. Here, we present circularized genome assemblies for two C. orientis-derived pathogens ( Bartonella clarridgeiae and R. asembonensis ) from Malaysia, a novel Wolbachia strain (wCori), and the C. orientis mitochondrion; all were obtained by direct metagenomic sequencing of flea tissues. Moreover, we isolated two Wolbachia strains from Malaysian C. felis into tick cell culture and recovered circularized genome assemblies for both, one of which (wCfeF) is newly sequenced. We demonstrate that the three Wolbachia strains are representatives of different major clades (‘supergroups’), two of which appear to be flea-specific. These Wolbachia genomes exhibit unique combinations of features associated with reproductive parasitism or mutualism, including prophage WO, cytoplasmic incompatibility factors and the biotin operon of obligate intracellular microbes. The first circularized assembly for R. asembonensis includes a plasmid with a markedly different structure and gene content compared to the published plasmid; moreover, this novel plasmid was also detected in cat flea metagenomes from the USA. Analysis of loci under positive selection in the transitional group revealed genes involved in host–pathogen interactions that may facilitate host switching. Finally, the first B. clarridgeiae genome from Asia exhibited large-scale genome stability compared to isolates from other continents, except for SNPs in regions predicted to mediate interactions with the vertebrate host. These findings highlight the paucity of data on the genomic diversity of Ctenocephalides-associated bacteria and raise questions regarding how interactions between members of the flea microbiome might influence vector competence.

Immune Reactions of Vector Insects to Parasites and Pathogens

“…Likewise, studies on C. felis injected with R. felis and using PCR showed that defensin-2, glycine-rich AMPs and several flea antigens were modulated by rickettsial infection [240]. Finally, apart from the bacterial pathogens transmitted, fleas are also known to have other bacteria in their microbiomes, but information is limited except that a diverse range of Wolbachia strains have been reported with unknown interactions with flea immunity and vector competence [244]. 1 and 3) There are ca.…”

Differentiation of Synanthropic Fleas from Andalusia (Spain) through Geometric Morphometrics Analysis

“…Fleas (Siphonaptera) comprise a highly specialized order of holometabolous ectoparasitic insects with a cosmopolitan distribution and about 2700 species described so far [ 1 ]. In addition to being able to provoke bites and pruritic welts on the skin, these arthropods are also known to be vectors of different pathogens, responsible for causing a wide variety of diseases worldwide, including bartonellosis, rickettsiosis, and bubonic plague [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. This is due to the nature of some flea species, which present a low host specificity that facilitates the exchanging of microorganisms, posing a potential threat to the health of both humans and animals [ 10 , 11 , 12 ].…”