# Comparative Genomics of the Endosymbiont Cardinium Causing Reproductive Manipulation in Encarsia Parasitoid Wasps

## TL;DR

This study sequenced four new genomes of the bacterium Cardinium, which manipulates the reproduction of parasitoid wasps, revealing insights into its genetic diversity and host interactions.

## Contribution

The paper presents four novel Cardinium genomes, including those associated with different reproductive manipulation phenotypes, and identifies candidate genes for host interaction.

## Key findings

- Cardinium strains in Encarsia wasps are more closely related to each other than to other Cardinium strains.
- Putative zinc finger proteins and a CI-related protein similar to Wolbachia's CidB were identified in the genomes.
- Three of the genomes contain predicted plasmids and horizontally transferred genes involved in metabolism.

## Abstract

Many invertebrates harbor the vertically transmitted endosymbiotic bacterium Cardinium hertigii, and some display altered reproductive phenotypes due to manipulation by Cardinium. Despite their host impact, genomic information for reproductive manipulator strains of Cardinium is sparse. Of the three reproductive manipulation phenotypes Cardinium is known to induce in its hosts, only two genomes causing cytoplasmic incompatibility (CI) are available, and genomes inducing other manipulation phenotypes are absent. In this study, we have sequenced and assembled four novel Cardinium genomes, three of which are associated with two different reproductive manipulation phenotypes, parthenogenesis induction and CI. Analysis of the genomes revealed that Cardinium associated with parasitoid wasp hosts in the genus Encarsia are generally more closely related to each other than to other Cardinium, but one strain, cEina2, is very similar to the whitefly‐associated Cardinium strain cBtQ1. Further, unique and shared candidate genes for host interaction were identified, including putative zinc finger proteins shared by the parthenogenesis‐associated strains cEper2 and cEhis1 and a large protein encoded by the CI Cardinium strain cEina3 with very distant similarity to the Wolbachia CI protein CidB. Finally, we predicted the presence of plasmids in three genomes. Also, despite the limited metabolic capacity of Cardinium, we identified potential horizontally transferred genes involved in central metabolism. These genomes will aid future studies to further our understanding of Cardinium‐induced reproductive manipulation.

We assembled four Cardinium hertigii draft genomes: cEina3 causes cytoplasmic incompatibility, cEhis1 induces parthenogenesis, cEper2 is associated with parthenogenesis, and cEina2 infects asymptomatically. All four strains are closely related and hosted by Encarsia parasitoid wasps, but key differences exist, including their metabolic potential and how they may interact with hosts.