Genome of Deadly Amoeba Sequenced -- Inman 2005 (224): 2 -- sciencenow:
Entamoeba histolytica infects up to 50 million people worldwide and causes amoebiasis--debilitating diarrhea and liver damage that kills an estimated 100,000 people per year. Among parasitic diseases, amoebiasis is second only to malaria in the numbers it affects and kills. Unlike other amoeba, which possess several types of intracellular compartments called organelles, E. histolytica contains only simple forms of two common organelles, the Golgi apparatus and endoplasmic reticulum. It also lacks the energy-generating mitochondria present in most living things and digests food with fermentation enzymes found only in bacteria and other very simple single-celled organisms. But researchers weren't sure if these were signs that the amoeba was primitive or if it had merely degenerated because of its parasitic lifestyle.
The complete genome of E. histolytica clears up the picture and offers some surprises. Led by scientists at The Institute for Genomic Research (TIGR) in Rockville, Maryland, and the Wellcome Trust Sanger Institute in the United Kingdom, the study indicates that the amoeba has snagged an astonishing 92 genes from bacteria in recent times, presumably by gobbling them up during its life in the human gut. A majority of these genes are involved in metabolism and presumably allow the amoeba to use bacterial metabolic pathways to adapt to the low oxygen environment of the gut. As a result, the amoeba could afford to loose its complex organelles.
Evolutionary hypotheses tested, and 100,000 people a year could be kept alive.