Research report

Wolbachia evolution: exploring the bacterial infection most widespread across the insect world

Matthias Scholz

The Wolbachia bacterium is one of the most abundant intracellular symbionts of nematodes, insects and other arthropods. It is estimated that about 40–60% of insect species are already infected with Wolbachia. Nevertheless, the interactions with its insect hosts are mostly mutualistic rather than parasitic. Even though the bacterium has strong impacts on host biology, ecology and evolution, including manipulation of host reproduction in order to increase its own spreading, some host species cannot anymore reproduce, or even survive, without Wolbachia infestation. For many insects, Wolbachia is an essential bacterial symbiont that acts as a nutritional mutualist, providing vitamins and nutrients that are important for host survival and strengthening the host immune system. By expanding extensively the number of available Wolbachia genomes, we want to create a detailed picture of the Wolbachia strain diversity, evolution, and how Wolbachia is spreading across different insect hosts. Together with scientists from the University of Trento we expanded the number of known Wolbachia genomes by screening over 30,000 publicly available shotgun sequencing data from more than 500 host species with a main focus on insect hosts. By assembling over 1000 of high quality genomes, we provide a large-scale collection of Wolbachia genomes that substantially increases host representation. We assembled many bacteria genomes for unrepresented species, including butterflies, bees, parasitoid wasps, and mites. Based on our large genome collection we created a huge phylogenetic tree that ultimately clarifies some open questions concerning Wolbachia strain diversity and bacteria-host co-evolution. We can show that each insect species is represented by its own branch of bacteria strains in the Wolbachia tree, confirming a strong functional adaptation of the bacterium to a new host. Each host species carries its own specific Wolbachia strain, well adapted to the host insect. Our genome comparison revealed several bacterial gene functions that are required for infecting certain insect hosts and for inducing specific phenotypes. Understanding Wolbachia diversity, host switch and functional adaptation to new insect hosts is not only interesting from the evolutionary point of view, it also has strong practical relevance. Infecting Anopheles mosquitoes permanently with a well adapted Wolbachia strain is a promising strategy to block the transmission of mosquito borne diseases including malaria and dengue fever.

Report Research and Innovation Centre 2019-2022 - Fondazione Edmund Mach