Hydrogenosomes were isolated, purified, biochemically characterized and named in the early 1970s by D. G. Lindmark and M. Müller at Rockefeller University. In addition to this seminal study on hydrogenosomes, they also demonstrated, for the first time, the presence of and hydrogenase in eukaryotes. Further studies were subsequently conducted on the biochemical cytology and subcellular organization of anaerobic protozoan parasites ''. It is often forgotten that a Czechoslovakian group also biochemically described hydrogenosomes in 1973. Using information obtained from hydrogenosomal and biochemical cytology studies these researchers determined the mode of action of metronidazole in 1976. Metronidazole is today recognized as the gold standardchemotherapeutic agent for the treatment of anaerobic infections caused by prokaryotes and eukaryotes. Metronidazole is taken up by diffusion. Once taken up by anaerobes, it is non-enzymatically reduced by reduced ferredoxin which is produced by the action of pyruvate:ferredoxin oxido-reductase. This reduction creates products toxic to the anaerobic cell, and allows for selective accumulation of the drug in anaerobes.
Description
Hydrogenosomes are approximately 1 micrometre in diameter but under stress conditions can reach up to 2 micrometres and are so called because they produce molecular hydrogen. Like mitochondria, they are bound by distinct double membranes and one has an inner membrane with some cristae-like projections. Hydrogenosomes have evolved from mitochondria by loss of aerobiosis-related features in several lineages. In most cases, hydrogenosomes are genomeless, though genomes have persisted in some lineages such as Neocallimastix, Trichomonas vaginalis or Tritrichomonas foetus. However, a hydrogenosomal genome has been detected in the cockroach ciliateNyctotherus ovalis, and the stramenopileBlastocystis. The similarity between Nyctotherus and Blastocystis, which are only distantly related, is believed to be the result of convergent evolution, and calls into question whether there is a clear-cut distinction between mitochondria, hydrogenosomes, and mitosomes.
In simple terms
One of the reasons that hydrogenosomes are of interest is because of the light they can cast on how life on earth may have evolved. Most life on earth is single celled, like Bacteria and Archaea. By contrast, plants and animals are made up of many cells. Crucially, each cell of a plant or animal is organised very differently from a bacterial cell. Amongst other things, animal and plant cells contain mitochondria. Mitochondria are like power stations for cells: They supply ATP molecules used throughout the cell as a power source by 'burning' carbohydrates and other fuels. They produce carbon dioxide and water as waste. To produce ATP, mitochondria require abundant supplies of oxygen. Some single-celled eukaryotes live in places where oxygen is scarce or non-existent and use hydrogenosomes instead of mitochondria to produce ATP. Mitochondria do not function with little or no oxygen, but hydrogenosomes are able to produce ATP from most of the same fuels without using oxygen. In addition to ordinary carbon dioxide, the distinctive waste product of hydrogenosomes is hydrogen: The hydrogen they produce gives the organelles their name. Hydrogenosomes are considered to be of scientific interest because comparing them with mitochondria may cast light on how all eukaryotic cells evolved. Hosting mitochondria appears to be a basal or near-basal trait among eukaryotes, the study of hydrogenosomes may shed light on how all multi-celled life developed. For example: Which came first: mitochondria, or hydrogenosomes, or some common ancestor?
