Potential horizontal gene transfer in Bathycoccus. (a) Taxonomic distribution of horizontal gene transfer (HGT) genes identified using BLAST and by phylogenetic analysis of each gene (excluding genes with a multi-kingdom punctuate distribution). Only taxonomic groups including multiple genes are displayed (for a complete overview, see Table S5 in Additional file 1). (b) Frequency of 428 HGT genes over the different chromosomes. The last bin reports the fraction of HGT genes in the BOC1 region (a subset of chromosome 14).