Coccidioides species determination: does sequence analysis agree with restriction fragment length polymorphism?

Area of Science:

• Mycology
• Molecular Biology
• Genetics

Background:

• Coccidioides fungal isolates exhibit genetic diversity.
• Previous restriction fragment length polymorphism (RFLP) analysis divided 15 isolates into two groups.
• Recent molecular studies established two distinct Coccidioides species: Coccidioides posadasii and Coccidioides immitis.

Purpose of the Study:

• To test the hypothesis that RFLP groupings correlate with the established species division of Coccidioides.
• To determine the species assignment for Coccidioides isolates using molecular methods.

Main Methods:

• Amplification and sequencing of the ribosomal DNA internal transcribed spacer region and three genes (dioxygenase, serine proteinase, urease) from 13 Coccidioides isolates.
• Phylogenetic analysis of sequencing data to assign species.
• Comparison of species assignments with previous RFLP groupings.

Main Results:

• Species assignment based on gene sequencing largely agreed with RFLP groupings.
• One isolate showed discordance, suggesting it may be a hybrid.
• Polymorphic sites across the four examined genes were consistent for species assignment.

Conclusions:

• The study supports the correlation between RFLP groups and Coccidioides species (C. posadasii and C. immitis).
• A potential hybrid Coccidioides isolate was identified.
• Analysis of a single gene may be sufficient for accurate species identification within the Coccidioides genus.