Variant calling results on a GCAT benchmark.

<p>Variant calling results on a GCAT benchmark.</p

Runtimes (in minutes) on simulated and real base-space reads.

<p>Runtimes (in minutes) on simulated and real base-space reads.</p

CUSHAW3: Sensitive and Accurate Base-Space and Color-Space Short-Read Alignment with Hybrid Seeding

<div><p>The majority of next-generation sequencing short-reads can be properly aligned by leading aligners at high speed. However, the alignment quality can still be further improved, since usually not all reads can be correctly aligned to large genomes, such as the human genome, even for simulated data. Moreover, even slight improvements in this area are important but challenging, and usually require significantly more computational endeavor. In this paper, we present CUSHAW3, an open-source parallelized, sensitive and accurate short-read aligner for both base-space and color-space sequences. In this aligner, we have investigated a hybrid seeding approach to improve alignment quality, which incorporates three different seed types, i.e. maximal exact match seeds, exact-match <i>k</i>-mer seeds and variable-length seeds, into the alignment pipeline. Furthermore, three techniques: weighted seed-pairing heuristic, paired-end alignment pair ranking and read mate rescuing have been conceived to facilitate accurate paired-end alignment. For base-space alignment, we have compared CUSHAW3 to Novoalign, CUSHAW2, BWA-MEM, Bowtie2 and GEM, by aligning both simulated and real reads to the human genome. The results show that CUSHAW3 consistently outperforms CUSHAW2, BWA-MEM, Bowtie2 and GEM in terms of single-end and paired-end alignment. Furthermore, our aligner has demonstrated better paired-end alignment performance than Novoalign for short-reads with high error rates. For color-space alignment, CUSHAW3 is consistently one of the best aligners compared to SHRiMP2 and BFAST. The source code of CUSHAW3 and all simulated data are available at <a href="http://cushaw3.sourceforge.net" target="_blank">http://cushaw3.sourceforge.net</a>.</p></div

Program workflow of the paired-end alignment with hybrid seeding.

<p>Program workflow of the paired-end alignment with hybrid seeding.</p

Alignment results on GCAT benchmarks.

<p>Alignment results on GCAT benchmarks.</p

Alignment quality and runtimes on color-space reads.

<p>Alignment quality and runtimes on color-space reads.</p

Real dataset information.

<p>Real dataset information.</p

Program workflow of the single-end alignment using hybrid seeding.

<p>Program workflow of the single-end alignment using hybrid seeding.</p

Alignment quality on simulated reads (in %).

<p>Alignment quality on simulated reads (in %).</p

Runtime (seconds) of the single-end alignment varying the number of nodes.

<p>Results are shown for the UPC++ implementation with static and on-demand distributions.</p