Metagenome-Assembled Genomes
One-Sentence Definition
Metagenome-assembled genomes (MAGs) are draft genomes reconstructed computationally from mixed-community sequencing by assembling and then binning contigs that belong to the same organism.
Simple Explanation
Sequence everything in a sample, assemble the pieces, then sort the pieces into piles — each pile is one organism’s genome, never cultured.
Detailed Scientific Explanation
Pipeline: reads → assembly (metaSPAdes, MEGAHIT) → binning (MetaBAT2, CONCOCT — using coverage + tetranucleotide frequency) → quality assessment (CheckM: completeness, contamination) → taxonomy (GTDB-Tk) → annotation.
Quality standards (MIMAG):
- High-quality draft: >90% complete, <5% contamination, with rRNA/tRNA present
- Medium-quality: ≥50% complete, <10% contamination
Limitations: strain mixtures collapse or fragment; mobile elements and rRNA operons are frequently lost; low-abundance taxa go unrecovered.
Mechanism
Contigs from the same genome share coverage profiles across samples and compositional signatures — clustering exploits both.
Clinical Importance
- Enables characterization of uncultured pathogens and gut community members implicated in disease
Research Importance
- Massively expanded the tree of life (Microbial Classification); discovered candidate phyla lacking cultured representatives
Diagnostic Relevance
- Research-grade today; clinical Metagenomics mostly uses read-level classification instead
AMR Relevance
- Linking resistance genes to their host organism is hard without binning — and still uncertain with it
Related MOCs
Active Recall Questions
- What two signals drive binning?
- What does CheckM estimate?
- Why is host attribution of AMR genes hard in metagenomes?