Genome assembly with Velvet. Reads are assembled into contigs using Velvet and VelvetOptimiser in two steps, (1) velveth converts reads to k-mers using a hash table, and (2) velvetg assembles overlapping k-mers into contigs via a de Bruijn graph. VelvetOptimiser can be used to automate the optimisation of parameters for velveth and velvetg and generate an optimal assembly. To generate an assembly of E. coli O104:H4 using the command-line tool Velvet: • Download Velvet  (we used version 1.2.08 on Mac OS X, compiled with a maximum k-mer length of 101 bp) • Download the paired-end Illumina reads for E. coli O104:H4 strain TY-2482 (ENA accession SRR292770 ) • Convert the reads to k-mers using this command: velveth out_data_35 35 -fastq.gz -shortPaired -separate SRR292770_1.fastq.gz SRR292770_2.fastq.gz • Then, assemble overlapping k-mers into contigs using this command: velvetg out_data_35 -clean yes -exp_cov 21 -cov_cutoff 2.81 -min_contig_lgth 200 This will produce a set of contigs in multifasta format for further analysis. See Additional file 1: Tutorial for further details, including help with downloading reads and using VelvetOptimiser.