Comparative Genomics of Two Closely Related Wolbachia with Different Reproductive Effects on Hosts

Area of Science:

• Microbiology
• Genomics
• Evolutionary Biology

Background:

• Wolbachia pipientis are intracellular bacteria influencing arthropod reproduction and immunity.
• They exhibit frequent horizontal transmission and high recombination rates.
• Wolbachia strains can induce diverse reproductive manipulations like cytoplasmic incompatibility and parthenogenesis.

Purpose of the Study:

• To compare the genomes of two closely related Wolbachia strains with distinct reproductive effects.
• To identify genomic changes associated with the shift from cytoplasmic incompatibility to parthenogenesis induction.
• To understand mutation patterns and selection pressures in Wolbachia.

Main Methods:

• Comparative genomics of two Wolbachia strains (wVitA and wUni).
• Analysis of genome-wide synonymous divergence (0.57%).
• Identification of rearrangements, protein truncations, and substitution rates.
• Investigation of gene loss and pseudogenization events.
• Estimation of mutation patterns and AT content bias.

Main Results:

• Rampant genomic rearrangements, protein truncations, and elevated substitution rates were observed, predominantly in the wUni lineage.
• The wUni lineage showed an approximately 8-fold elevated synonymous substitution rate compared to wVitA.
• Specific gene losses and pseudogenizations in wUni were linked to the shift towards parthenogenesis induction.
• Mutation probabilities at 4-fold degenerate sites were not AT-biased, contrasting with the high AT content of Wolbachia genomes.

Conclusions:

• Genomic plasticity and specific gene evolution in the wUni lineage likely underlie its parthenogenetic induction phenotype.
• Elevated substitution rates in wUni may be driven by increased mutation rate or more generations per year in its semitropical host.
• Wolbachia genomes show evidence of selection for increased AT content, despite mutation probabilities not being AT-biased.