Hydrogen hypothesis
From Wikipedia, the free encyclopedia
The hydrogen hypothesis is a model proposed by William Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion developed in the first eukaryotic cell within the endosymbiotic theory framework.
According to the hydrogen hypothesis the first eukaryotic cell did not appear as a consequence of a primitive host cell engulfing a primitive bacterium that eventually became the mitochondrion, as the endosymbiotic theory suggests. It claims instead that the host - a methanogenic archaebacterium, which used hydrogen and carbon dioxide to produce methane - and a facultatively anaerobic eubacterium, the future mitochondrion, which produced hydrogen and carbon dioxide as byproducts of anaerobic respiration, started a symbiotic relationship based on the host's hydrogen dependence (anaerobic syntrophy).
The idea originated when Martin attended a talk by Müller on hydrogenosomes. These are anaerobic mitochondria that produce ATP and large amounts of hydrogen and carbon dioxide. One of Müller's slides presented a cluster of methanogens around a hydrogenosome inside a eukaryotic cell they had invaded.
If correct, this hypothesis would imply that eukaryotes are chimeras with archaebacterial and eubacterial ancestry. It would furthermore imply that eukaryotes appeared later in evolution than prokaryotes. This contrasts with some views that assume archaea and eukarya split before the modern groups of archaea appeared. The hydrogen hypothesis postulates that no mitochondrion-lacking eukaryotes ever existed.
[edit] References
- López-Garćia P, Moreira D. (1999). "Metabolic symbiosis at the origin of eukaryotes.". Trends Biochem Sci. 24 (3): 88-93. doi:.
- Martin W. and Müller M. (1998). "The hydrogen hypothesis for the first eukaryote". Nature 392 (6671): 37-41. doi:.
- Poole AM. and Penny D. (2007). "Evaluating hypotheses for the origin of eukaryotes.". Bioessays 29 (1): 74-84. doi:.
