OTU / ASV
Definition
Operational Taxonomic Unit (OTU) and Amplicon Sequence Variant (ASV) are the units of microbial diversity in 16S data. OTUs cluster reads at 97% sequence similarity; ASVs resolve single-nucleotide differences and are increasingly preferred for forensic work due to finer resolution.
- OTU clustering threshold
- 97% sequence similarity
- ASV resolution
- Single-nucleotide differences
- Data source
- 16S rRNA microbial sequencing
- Forensic trend
- ASVs increasingly preferred for finer resolution
Common questions
Why does the OTU-versus-ASV choice matter for forensic microbiome evidence?+
ASVs preserve exact sequence variants rather than binning similar reads together, which improves reproducibility across different sequencing runs and labs, a property that matters when microbiome profiles are compared as evidence over time.
Can OTU-based and ASV-based studies be directly compared?+
Not without care. Because OTUs collapse near-identical sequences at a fixed similarity cutoff while ASVs keep them distinct, results from the two approaches can show different diversity counts for the same underlying sample.
Related terms
- 16S rRNA Gene
- The gene encoding the 16S ribosomal RNA subunit present in all bacteria and archaea. Conserved regions allow universal amplification; hypervariable regions (V1-V9)...
- Amplicon Sequencing
- A sequencing approach where a specific locus (here the 16S hypervariable region) is amplified from all members of a microbial community and...
- Community State Type (CST)
- A classification of vaginal microbiome profiles into distinct clusters. Most CSTs are dominated by a single Lactobacillus species; one CST (often called...
- Microbiome
- The total community of microorganisms (bacteria, archaea, fungi, viruses) inhabiting a body site, along with their collective genetic material. Each body site...
- Shotgun Metagenomics
- Sequencing all DNA in a sample rather than just the 16S amplicon. Provides taxonomic resolution beyond 16S and can characterise viruses and...