Hydrogenosome

From Freepedia

A hydrogenosome is an organelle of ciliates, trichomonads and fungi. It produces hydrogen and ATP. This organelle would have evolved from mitochondria.

Certain anaerobic protozoa and fungi possess membrane-bound organelles known as "hydrogenosomes". Hydrogenosomes have been discovered in the early 70s by Lindmark and Müller in the US and by Kulda and others in Prague. These organelles are approximately 1 micrometre in diameter and are so called because they produce molecular hydrogen. The anaerobic *ciliate protozoan Nyctotherus ovalis, found in the hindgut of several species of cockroach, has numerous hydrogenosomes that are intimately associated with *endosymbiotic methane-producing *Archaea, the latter using the hydrogen produced by the hydrogenosomes.

The best studied hydrogenosomes are those of the sexually transmitted parasite Trichomonas vaginalis and those from rumen chytrids such as Neocallimastix.

Like mitochondria, the hydrogenosomes are bound by distinct double membranes and have an inner membrane with some *cristae-like projections.

It had been postulated that hydrogenosomes evolved from mitochondria by the concomitant loss of their respiration and organellar genomes, and indeed so far no hydrogenosome has been found that has a genome.

The matrix of N. ovalis hydrogenosomes contains *ribosome-like particles of the same size as a numerous type of ribosome (70s) of the endosymbiotic methanogenic Archaea. This suggested the presence of an organellar genome which was discovered indeed by Akhmanova et al (Nature 1998 396:527) and later partly sequenced by Boxma et al (Nature 2005 434: 74-79).

This finding was the final confirmation that hydrogenosomes are indeed derived from mitochondria (see for example van der Giezen et al Int Rev Cytol 244: 175-225).