Evolution of Wolbachia mutualism and reproductive parasitism: insight from two novel strains that co-infect cat fleas

Wolbachiae 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 and wCfeJ, found co-infecting cat fleas (Ctenocephalides felis) of the Elward Laboratory colony (Soquel, CA, USA). wCfeT is basal to nearly all described Wolbachia supergroups, while wCfeJ is related to supergroups C, D and F. Both genomes contain laterally transferred genes that inform on the evolution of Wolbachia host associations. wCfeT carries the Biotin synthesis Operon of Obligate intracellular Microbes (BOOM); our analyses reveal five independent acquisitions of BOOM across the Wolbachia tree, indicating parallel evolution towards mutualism. Alternately, wCfeJ harbors a toxin-antidote operon analogous to the wPip cinAB operon recently characterized as an inducer of cytoplasmic incompatibility (CI) in flies. wCfeJ cinB and three adjacent genes are collectively similar to large modular toxins encoded in CI-like operons of certain Wolbachia strains and Rickettsia species, signifying that CI toxins streamline by fission of large modular toxins. Remarkably, the C. felis genome itself contains two CI-like antidote genes, divergent from wCfeJ cinA, 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) amongst C. felis colonies, though fleas in wild populations mostly harbor wCfeT alone. Collectively, genomes of wCfeT, wCfeJ, and their cat flea host supply instances of lateral gene transfers that could drive transitions between parasitism and mutualism.

Parthenogenesis in weevils of the tribe Naupactini (Coleoptera, Curculionidae): a Wolbachia-density dependent trait?

The intracellular bacteria Wolbachia pipientis can manipulate host reproduction to enhance their vertical transmission. It has been reported an association between parthenogenesis and Wolbachia infection in weevils from the tribe Naupactini. A curing experiment suggested that a threshold density of Wolbachia is required for parthenogenesis to occur. The aim of this study was to analyze Wolbachia infection status in the bisexual species Naupactus xanthographus and Naupactus dissimulator.Wolbachia infection was detected in both species from some geographic locations, not being fixed. In all positive cases, faint PCR bands were observed. Quantification through real time PCR confirmed that Wolbachia loads in bisexual species were significantly lower than in parthenogenetic ones; this strengthens the hypothesis of a threshold level. Strain typing showed that both species carry wNau1, the most frequent in parthenogenetic Naupactini weevils. These infections seem to be recently acquired by horizontal transfer. Wolbachia was located throughout the whole body, which reinforce the idea of recent transmission. Moreover, we demonstrated that this strain carries the WO phage.Finally, the analysis of eubacterial 16S rRNA gene showed intense PCR bands for both bisexual species, suggesting –the presence of additional bacteria. Interspecific competition might explain why the parthenogenetic phenotype is not triggered.

High-Efficiency Thermal Asymmetric Interlaced PCR (hiTAIL-PCR) for Determination of a Highly Degenerated Prophage WO Genome in a Wolbachia Strain Infecting a Fig Wasp Species

ABSTRACTTemperate bacteriophage WO is a model system for studying tripartite interactions among viruses, bacteria, and eukaryotes, especially investigations of the genomic stability of obligate intracellular bacteria. Few WO genomes exist because of the difficulty in isolating viral DNA from eukaryotic hosts, and most reports are by-products ofWolbachiasequencing. Only one partial genome of a WO phage has been determined directly from isolated particles. We determine the complete genome sequence of prophage WO (WOSol) inWolbachiastrainwSol, which infects the fig waspCeratosolen solmsi(Hymenoptera: Chalcidoidea), by high-efficiency thermal asymmetric interlaced PCR. The genome of WOSol is highly degenerated and disrupted by a large region (14,267 bp) fromWolbachia. Consistent with previous molecular studies of multiple WO genomes, the genome of WOSol appears to have evolved by single nucleotide mutations and recombinations.