Amoebozoa Possess Lineage-Specific Globin Gene Repertoires Gained by Individual Horizontal Gene Transfers

Abstract

The Amoebozoa represent a clade of unicellular amoeboid organisms that display a wide variety of lifestyles, including free-living and parasitic species. For example, the social amoeba Dictyostelium discoideum has the ability to aggregate into a multicellular fruiting body upon starvation, while the pathogenic amoeba Entamoeba histolytica is a parasite of humans. Globins are small heme proteins that are present in almost all extant organisms. Although several genomes of amoebozoan species have been sequenced, little is known about the phyletic distribution of globin genes within this phylum. Only two flavohemoglobins (FHbs) of D. discoideum have been reported and characterized previously while the genomes of Entamoeba species are apparently devoid of globin genes. We investigated eleven amoebozoan species for the presence of globin genes by genomic and phylogenetic in silico analyses. Additional FHb genes were identified in the genomes of four social amoebas and the true slime mold Physarum polycephalum. Moreover, a single-domain globin (SDFgb) of Hartmannella vermiformis, as well as two truncated hemoglobins (trHbs) of Acanthamoeba castellanii were identified. Phylogenetic evidence suggests that these globin genes were independently acquired via horizontal gene transfer from some ancestral bacteria. Furthermore, the phylogenetic tree of amoebozoan FHbs indicates that they do not share a common ancestry and that a transfer of FHbs from bacteria to amoeba occurred multiple times.

The aerotaxis of Dictyostelium discoideum is independent of mitochondria, nitric oxide and oxidative stress

“…Dictyostelium genome encodes two flavohemoglobins genes, fhbA and fhbB , that were successfully inactivated ( Iijima et al, 2000 ). Dictyostelium flavohemoglobin proteins share well conserved amino-acid sequences and structure with the characterized bacterial and fungal homologs shown to act as NO dioxygenases ( Dröge et al, 2014 ). While the enzymatic activity of FhbA and FhbB has not been tested, the double null mutant fhbA - B - displays poor viability when challenged with NO generating chemicals, consistent with their expected NO dioxygenases functions ( Iijima et al, 2000 ).…”