ScienceDaily (July 26, 2001) — NWO researchers have discovered that in the course of evolution hydrogenosomes repeatedly evolved from mitochondria. Hydrogenosomes, or ‘hydrogen-forming organelles’, are cell organelles that produce hydrogen and energy. They serve as an alternative energy supply in organisms that live without oxygen, such as anaerobic fungi and protozoa.

The microbiologists believe that hydrogenosomes evolved from mitochondria as a result of a drastic ecological change. Protozoans and fungi, which until then had lived in an oxygen-rich environment, found themselves in a completely anoxic environment. Without oxygen the potential of the mitochondria to produce energy is rather limited.

In order to survive, the micro-organisms evolved several alternative means of energy production. One way of doing this was to convert mitochondria into hydrogenosomes. This required genetic material from bacteria that can survive in an anoxic environment. This genetic material was transferred from one micro-organism to another by means of ‘lateral gene transfer’.

The research team compared the hydrogenosomes of various protozoans and anaerobic fungi and discovered that the contents and form of these cell organelles differ from species to species. The hydrogenosomes of Nyctotherus ovalis, a protozoan from the gut of the cockroach, still very much resemble mitochondria. Those of Neocallimastix and Piromyces, fungi from the gut of the llama and the Indian elephant, look entirely different.

Besides the differences, there are also many points of similarity between the hydrogenosomes of different species. The researchers concluded that the hydrogenosomes of the different species constantly evolved anew from mitochondria in the course of evolution.

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