Thursday, 14 June 2012

SEQuel: improving the accuracy of genome assemblies.

Bioinformatics. 2012 Jun 15;28(12):i188-i196.
SEQuel: improving the accuracy of genome assemblies.
Ronen R, Boucher C, Chitsaz H, Pevzner P.

Bioinformatics Graduate Program, Department of Computer Science and Engineering, University of California, San Diego, La Jolla, CA 92093 and Department of Computer Science, Wayne State University, Detroit, MI 48202, USA.


Assemblies of next-generation sequencing (NGS) data, although accurate, still contain a substantial number of errors that need to be corrected after the assembly process. We develop SEQuel, a tool that corrects errors (i.e. insertions, deletions and substitution errors) in the assembled contigs. Fundamental to the algorithm behind SEQuel is the positional de Bruijn graph, a graph structure that models k-mers within reads while incorporating the approximate positions of reads into the model.


SEQuel reduced the number of small insertions and deletions in the assemblies of standard multi-cell Escherichia coli data by almost half, and corrected between 30% and 94% of the substitution errors. Further, we show SEQuel is imperative to improving single-cell assembly, which is inherently more challenging due to higher error rates and non-uniform coverage; over half of the small indels, and substitution errors in the single-cell assemblies were corrected. We apply SEQuel to the recently assembled Deltaproteobacterium SAR324 genome, which is the first bacterial genome with a comprehensive single-cell genome assembly, and make over 800 changes (insertions, deletions and substitutions) to refine this assembly.


SEQuel can be used as a post-processing step in combination with any NGS assembler and is freely available at


PMID: 22689760 [PubMed - in process]

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