Rickettsia induces strong cytoplasmic incompatibility in a predatory insect

Rickettsia, a group of intracellular bacteria found in eukaryotes,
exhibits diverse lifestyles, with some acting as vertebrate pathogens
transmitted by arthropod vectors and others serving as maternally
transmitted arthropod endosymbionts, some of which manipulate host
reproduction for their own benefit. Two phenotypes, namely male killing
and parthenogenesis induction are known as Rickettsia-induced host
reproductive manipulations, but it remains unknown whether Rickettsia can
induce other types of host manipulation. In this study, we discovered that
Rickettsia induced strong cytoplasmic incompatibility (CI), in which
uninfected females produce no offspring when mated with infected males, in
the predatory insect Nesidiocoris tenuis (Hemiptera: Miridae). Molecular
phylogenetic analysis revealed that the Rickettsia strain was related to
Rickettsia bellii, a common insect endosymbiont. Notably, this strain
carried plasmid-encoded homologues of the CI-inducing factors (namely
cifA-like and cifB-like genes), typically found in Wolbachia, which are
well-known CI-inducing endosymbionts. Protein domain prediction revealed
that the cifB-like gene encodes PD-(D/E)XK nuclease and deubiquitinase
domains, which are responsible for Wolbachia-induced CI, as well as
OTU-like cysteine protease and ankyrin repeat domains. These findings
suggest that Rickettsia and Wolbachia endosymbionts share underlying
mechanisms of CI and that CI-inducing ability was acquired by microbes
through horizontal plasmid transfer.