Endosymbiotic Rickettsiella causes cytoplasmic incompatibility in a spider host

Many arthropod hosts are infected with bacterial endosymbionts that manipulate host reproduction, but few bacterial taxa have been shown to cause such manipulations. Here, we show that a bacterial strain in the genusRickettsiellacauses cytoplasmic incompatibility (CI) between infected and uninfected hosts. We first surveyed the bacterial community of the agricultural spiderMermessus fradeorum(Linyphiidae) using high throughput sequencing and found that individual spiders can be infected with up to five different strains of maternally inherited symbiont from the generaWolbachia,Rickettsia, andRickettsiella. TheRickettsiellastrain was pervasive, found in all 23 tested spider matrilines. We used antibiotic curing to generate uninfected matrilines that we reciprocally crossed with individuals infected only withRickettsiella. We found that only 13% of eggs hatched when uninfected females were mated withRickettsiella-infected males; in contrast, at least 83% of eggs hatched in the other cross types. This is the first documentation ofRickettsiella, or any Gammaproteobacteria, causing CI. We speculate that induction of CI may be much more widespread among maternally inherited bacteria than previously appreciated. Further, our results reinforce the importance of thoroughly characterizing and assessing the inherited microbiome before attributing observed host phenotypes to well-characterized symbionts such asWolbachia.