Pooled samples bias fungal community descriptions

Area of Science:

• Mycology
• Molecular Ecology
• Bioinformatics

Background:

• Accurate assessment of fungal community structure and species richness is crucial for ecological research.
• Molecular techniques are increasingly used to study microbial communities, but their accuracy with pooled samples requires validation.

Purpose of the Study:

• To evaluate the accuracy of different molecular methods in determining species richness and community structure from pooled fungal samples.
• To identify potential biases and errors introduced by sample pooling and DNA extraction procedures in fungal community analysis.

Main Methods:

• Construction of replicate pooled fungal communities with known species compositions (2-20 species).
• Application of two DNA extraction protocols and three molecular analyses: Automated Ribosomal Intergenic Spacer Analysis (ARISA), terminal restriction fragment length polymorphism (T-RFLP), and clone library sequencing.
• Comparison of molecular results against the known community composition to assess accuracy.

Main Results:

• No molecular method accurately reconstructed the known fungal communities.
• Clone library sequencing, with approximately 100 clones sequenced per pool, provided the most reasonable estimates of species richness.
• All tested procedures and analyses resulted in skewed frequency data, indicating significant biases.

Conclusions:

• Sample pooling introduces substantial errors that complicate the ecological interpretation of fungal community data.
• Current molecular methods, including ARISA and T-RFLP, are unreliable for quantifying fungal species richness and structure in pooled samples.
• High sequencing depth in clone libraries is necessary but may not fully overcome biases associated with sample pooling in fungal community ecology.