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De novo assembler for single molecule sequencing reads using repeat graphs

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Flye assembler

BioConda Install

Version: 2.6

Flye is a de novo assembler for single molecule sequencing reads, such as those produced by PacBio and Oxford Nanopore Technologies. It is designed for a wide range of datasets, from small bacterial projects to large mammalian-scale assemblies. The package represents a complete pipeline: it takes raw PB / ONT reads as input and outputs polished contigs. Flye also includes a special mode for metagenome assembly.

Latest updates

Flye 2.6 release (19 Sep 2019)

  • This release introduces Python 3 support (no other changes)

Flye 2.5 release (25 Jul 2019)

  • Better ONT polishing for the latest basecallers (Guppy/flipflop)
  • Improved consensus quality of repetitive regions
  • More contiguous assemblies of real metagenomes
  • Improvements for human genome assemblies
  • Various bugfixes and performance optimizations
  • Also check the new FAQ section

Manuals

Repeat graph

Flye is using repeat graph as a core data structure. In difference to de Bruijn graphs (which require exact k-mer matches), repeat graphs are built using approximate sequence matches, and can tolerate higher noise of SMS reads.

The edges of repeat graph represent genomic sequence, and nodes define the junctions. Each edges is classified into unique or repetitive. The genome traverses the graph (in an unknown way), so as each unique edge appears exactly once in this traversal. Repeat graphs reveal the repeat structure of the genome, which helps to reconstruct an optimal assembly.

Graph example

Above is an example of the repeat graph of a bacterial assembly. Each edge is labeled with its id, length and coverage. Repetitive edges are shown in color, and unique edges are black. Note that each edge is represented in two copies: forward and reverse complement (marked with +/- signs), therefore the entire genome is represented in two copies. This is necessary because the orientation of input reads is unknown.

In this example, there are two unresolved repeats: (i) a red repeat of multiplicity two and length 35k and (ii) a green repeat cluster of multiplicity three and length 34k - 36k. As the repeats remained unresolved, there are no reads in the dataset that cover those repeats in full. Five unique edges will correspond to five contigs in the final assembly.

Repeat graphs produced by Flye could be visualized using AGB or Bandage.

Flye benchmarks

Genome Data Asm.Size NG50 CPU time RAM
E.coli PB 50x 4.6 Mb 4.6 Mb 2 h 2 Gb
C.elegans PB 40x 102 Mb 2.9 Mb 100 h 31 Gb
A.thaliana PB 75x 120 Mb 10.7 Mb 100 h 46 Gb
D.melanogaster ONT 30x 139 Mb 17.5 Mb 130 h 31 Gb
D.melanogaster PB 120x 142 Mb 17.5 Mb 150 h 75 Gb
Human NA12878 ONT 35x (rel6) 2.9 Gb 22.6 Mb 2500 h 714 Gb
Human CHM13 T2T ONT 50x (rel2) 2.9 Gb 57.9 Mb 3600 h 871 Gb
Human HG002 PB CCS 30x 2.9 Gb 30.4 Mb 1400 h 272 Gb
Human CHM1 PB 100x 2.8 Gb 18.8 Mb 2700 h 676 Gb
HMP mock PB meta 7 Gb 66 Mb 2.6 Mb 60 h 72 Gb
Zymo Even ONT meta 14 Gb 64 Mb 0.6 Mb 60 h 129 Gb
Zymo Log ONT meta 16 Gb 23 Mb 1.3 Mb 100 h 76 Gb

The assemblies generated using Flye 2.5 could be downloaded from Zenodo. All datasets were run with default parameters with the following exceptions: CHM13 T2T was run with --min-overlap 10000; CHM1 was run with --asm-overage 40; HG002 was run with maximum read error rate set to 1%.

Third-party

Flye package includes some third-party software:

License

Flye is distributed under a BSD license. See the LICENSE file for details.

Credits

Flye is developed in Pavel Pevzner's lab at UCSD

Code contributions:

  • Repeat graph and current package maintaining: Mikhail Kolmogorov
  • Trestle module and original polisher code: Jeffrey Yuan
  • Original contig extension code: Yu Lin
  • Short plasmids recovery module: Evgeny Polevikov

Publications

Mikhail Kolmogorov, Jeffrey Yuan, Yu Lin and Pavel Pevzner, "Assembly of Long Error-Prone Reads Using Repeat Graphs", Nature Biotechnology, 2019 doi:10.1038/s41587-019-0072-8

Yu Lin, Jeffrey Yuan, Mikhail Kolmogorov, Max W Shen, Mark Chaisson and Pavel Pevzner, "Assembly of Long Error-Prone Reads Using de Bruijn Graphs", PNAS, 2016 doi:10.1073/pnas.1604560113

How to get help

A preferred way report any problems or ask questions about Flye is the issue tracker. Before posting an issue/question, consider to look through the FAQ and existing issues (opened and closed) - it is possble that your question has already been answered.

If you reporting a problem, please include the flye.log file and provide some details about your dataset (if possible).

In case you prefer personal communication, please contact Mikhail at [email protected].

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