Motivation: Why recombination? is one of the central questions in biology. This has led to a host of methods for quantifying recombination from sequence data. These methods are usually based on aligned DNA sequences. Here, we propose an efficient alignment-free alternative.

Results: Our method is based on the distribution of match lengths, which we look up using enhanced suffix arrays. By eliminating the alignment step, the test becomes fast enough for application to whole bacterial genomes. Using simulations we show that our test has similar power as established tests when applied to long pairs of sequences. When applied to 58 genomes of Escherichia coli, we pick up the strongest recombination signal from a 125 kb horizontal gene transfer engineered 20 years ago.

Availability and implementation: We have implemented our method in the command-line program rush. Its C sources and documentation are available under the GNU General Public License from

Contact:  [email protected]

Supplementary information:  Supplementary data are available at Bioinformatics online.