Identification of cytoplasmic incompatibility effectors of the reproductive manipulator Cardinium hertigii

Cytoplasmic incompatibility (CI), a widespread symbiont-induced reproductive manipulation phenotype in arthropods, selectively kills embryonic offspring produced when infected males mate with uninfected females. Most knowledge on CI comes from studying the Pseudomonadota symbiont Wolbachia and their CI effector (cif) genes, and little is known about CI mechanisms of symbionts without cif genes. We identify two putative CI effectors of Cardinium hertigii cEper1, a Bacteroidota symbiont of the parasitoid wasp Encarsia suzannae, using a combined proteomics and heterologous expression approach. We show that these genes, CAHE_0406 and CAHE_p0043, have no homology to known cif genes, yet impair yeast growth similar to known cifs and that CAHE_p0043 localizes to diffuse and fragmented yeast nuclei. These results suggest that CAHE_0406 and/or CAHE_p0043 could play a role in cEper1-induced CI, expanding our current understanding of the diversity of proteins involved in cytoplasmic incompatibility across symbiont lineages.