RAPPAS

RAPPAS performs alignment-free phylogenetic placement of environmental DNA and metagenomic short reads by using a precomputed k-mer database to assign query sequences to positions on a reference phylogenetic tree for taxonomic classification and diagnostics.

Key Features:

• Alignment-free placement: Eliminates the need for preliminary sequence alignment by using k-mer–based comparisons.
• Precomputed k-mer database: Uses a database of k-mers derived from reference sequences to represent sequence information without alignment.
• Phylogenetic origin annotation: Associates each stored k-mer with phylogenetic origin information and probabilities.
• Probabilistic placement: Determines query placement by examining k-mers' stored phylogenetic origins and their associated probabilities.
• Scalability for high-throughput sequencing: Designed to scale to large datasets generated by high-throughput sequencing technologies.
• Accuracy for short reads: Maintains placement accuracy comparable to likelihood-based phylogenetic placement methods, particularly for short reads.
• Reusable databases: Supports reuse of the precomputed k-mer database across multiple metagenomic analyses.

Scientific Applications:

• Environmental DNA analysis: Assignment of environmental DNA sequences to positions on a reference phylogeny for biodiversity studies.
• Taxonomic classification: Taxonomic assignment of query sequences via phylogenetic placement on a reference tree.
• Metagenomic diagnostics: Rapid phylogenetic placement for diagnostic applications requiring precise origin assignment of sequences.
• High-throughput short-read placement: Placement of short reads from high-throughput sequencing within a phylogenetic framework.

Methodology:

Uses a precomputed database of k-mers annotated with phylogenetic origins and associated probabilities and determines placement of query sequences by examining those stored origins and probabilities while avoiding preliminary sequence alignment; the k-mer database is reusable across analyses.