Functional categories of identified lateral gene transfer (LGTs). (a) Distribution of functional annotation from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database of LGTs supported by at least one node (357 entries; see Additional file 2; see Additional file 5). In total, 220 enzymes were identified, of which 165 (75%) could be mapped onto a KEGG pathway. The 'Other Metabolic Pathways' category includes the following KEGG pathways: 'Signal Transduction,' 'Metabolism of Secondary Metabolites,' and 'Metabolism of Terpenoids and Polyketides.' In total, 49 enzymes, labeled as 'Enzyme Reactions,' are not part of any metabolic pathway. Hypothetical proteins and poorly characterized entries are pooled in the category 'Hypothetical Proteins'. The number of entries in each functional category is based on the number of LGT events rather than genes, with an ancient LGT counted once. (b,c) Comparison of functional characterization of LGTs for (b) extracellular mucosal parasites (Trichomonas vaginalis, Entamoeba histolytica, Giardia lamblia) versus insect-transmitted blood parasites (Trypanosoma brucei, Trypanosoma cruzi, Plasmodium falciparum, Plasmodium vivax, Plasmodium yoelii yoelii) and (c) the parasitic amoebozoan E. histolytica versus the free-living amoebozoan Dictyostelium discoideum. Fisher's exact test was performed to test the null hypothesis that functional annotations of LGTs are distributed equally between the compared taxa. The P-values for the tests are indicated. The numbers of LGTs for each set of taxa are indicated between brackets.