Evolution ofWolbachiaMutualism and Reproductive Parasitism: Insight from Two Novel Strains that Co-infect Cat Fleas

Abstract

AbstractWolbachiae are obligate intracellular bacteria that infect arthropods and certain nematodes. Usually maternally inherited, they may provision nutrients to (mutualism) or alter sexual biology of (reproductive parasitism) their invertebrate hosts. We report the assembly of closed genomes for two novel wolbachiae,wCfeT andwCfeJ, found co-infecting cat fleas (Ctenocephalides felis) of the Elward Laboratory colony (Soquel, CA).wCfeT is basal to nearly all describedWolbachiasupergroups, whilewCfeJ is related to supergroups C, D and F. Both genomes contain laterally transferred genes that inform on the evolution ofWolbachiahost associations.wCfeT carries the Biotin synthesis Operon of Obligate intracellular Microbes (BOOM); our analyses reveal five independent acquisitions of BOOM across theWolbachiatree, indicating parallel evolution towards mutualism. Alternately,wCfeJ harbors a toxin-antidote operon analogous to thewPipcinABoperon recently characterized as an inducer of cytoplasmic incompatibility (CI) in flies.wCfeJcinBand immediate-5’ end genes are syntenic to large modular toxins encoded in CI-like operons of certainWolbachiastrains andRickettsiaspecies, signifying that CI toxins streamline by fission of larger toxins. Remarkably, theC.felisgenome itself contains two CI-like antidote genes, divergent from wCfeJcinA, revealing episodic reproductive parasitism in cat fleas and evidencing mobility of CI loci independent of WO-phage. Additional screening revealed predominant co-infection (wCfeT/wCfeJ) amongstC.feliscolonies, though occasionallywCfeJ singly infects fleas in wild populations. Collectively, genomes ofwCfeT,wCfeJ, and their cat flea host supply instances of lateral gene transfers that could drive transitions between parasitism and mutualism.ImportanceMany arthropod and certain nematode species are infected with wolbachiae which are intracellular bacteria well known for reproductive parasitism (RP). Like other RP strategies,Wolbachia-induced cytoplasmic incompatibility, CI, increases prevalence and frequency in host populations. Mutualism is another strategy employed by wolbachiae to maintain host infection, with some strains synthesizing and supplementing certain B vitamins (particularly biotin) to invertebrate hosts. Curiously, we discovered two novelWolbachiastrains that co-infect cat fleas (Ctenocephalides felis):wCfeT carries biotin synthesis genes, whilewCfeJ carries a CI-inducing toxin-antidote operon. Our analyses of these genes highlight their mobility across theWolbachiaphylogeny and source to other intracellular bacteria. Remarkably, theC.felisgenome also carries two CI-like antidote genes divergent from thewCfeJ antidote gene, indicating episodic RP in cat fleas. Collectively,wCfeT andwCfeJ inform on the rampant dissemination of diverse factors that mediateWolbachiastrategies for persisting in invertebrate host populations.