Counting rare Wolbachia endosymbionts using digital droplet PCR

Area of Science:

• Microbiology
• Genetics
• Entomology

Background:

• Wolbachia is a widespread intracellular microbe in insects, crucial for pathogen suppression and disease control.
• Accurate quantification of Wolbachia abundance is vital for understanding its role in host-pathogen dynamics and population spread.
• Quantitative polymerase chain reaction (qPCR) has limitations in detecting low Wolbachia levels, often requiring sample pooling and losing individual resolution.

Purpose of the Study:

• To develop and validate highly sensitive digital droplet PCR (ddPCR) assays for quantifying Wolbachia.
• To establish methods for measuring total Wolbachia abundance, DNA extraction efficiency-adjusted abundance, and Wolbachia density relative to host genome copies.
• To assess the broad applicability of these ddPCR assays across diverse Wolbachia strains and host species.

Main Methods:

• Development of three distinct ddPCR assays targeting Wolbachia-specific genes.
• Validation of assay sensitivity using Drosophila melanogaster infected with wMel Wolbachia.
• Testing oligo homology against a wide range of Wolbachia strains and host species.

Main Results:

• The developed ddPCR assays can reliably detect as few as 7–12 Wolbachia gene copies per reaction.
• Assays demonstrate high sensitivity, eliminating the need for sample pooling.
• Oligos show homology to numerous Wolbachia strains (Supergroup A) and host species across Drosophila, Scaptomyza, and Zaprionus genera.

Conclusions:

• Highly sensitive ddPCR assays significantly advance Wolbachia-host interaction research.
• These assays enable molecular data collection from individual insect tissues, crucial for understanding Wolbachia dynamics.
• The ability to detect rare Wolbachia is particularly valuable for field applications and studying natural populations.