Early lateral transfer of genes encoding malic enzyme, acetyl-CoA synthetase and alcohol dehydrogenases from anaerobic prokaryotes to Entamoeba histolytica

The fermentation enzymes, which enable the microaerophilic protist Entamoeb a histolytica to parasitize the colonic lumen and tissue abscesses, closely resemble homologues in anaerobic prokaryotes. Here, genes encoding malic e nzyme and acetyl-CoA synthetase (nucleoside diphosphate forming) were clone d from E. histolytica, and their evolutionary origins, as well as those enc oding two alcohol dehydrogenases (ADHE and ADH1), were inferred by means of phylogenetic reconstruction. The E. histolytica malic enzyme, which decarb oxylates malate to pyruvate, closely resembles that of the archaeon Archaeo globus fulgidus, strongly suggesting a common origin. The E. histolytica ac etyl-CoA synthetase, which converts acetyl-CoA to acetate with the producti on of ATP, appeared to be closely related to the Plasmodium falciparum enzy me, but it was no more closely related to the Giardia lamblia acetyl-CoA sy nthetase than to those of archaea. Phylogenetic analyses suggested that the adh1 and adhe genes of E. histolytica and Gram-positive eubacteria share a common ancestor. Lateral transfer of genes encoding these fermentation enz ymes from archaea or eubacteria to E. histolytica probably occurred early, because the sequences of the amoebic enzymes show considerable divergence f rom those of prokaryotes, and the amoebic genes encoding these enzymes are in the AT-rich codon usage of the parasite.