The mitochondrion lies at the heart of eukaryotic cell biology, with key roles in energy production, apoptosis, free radical biology and intermediary metabolism. Fully integrated into the life of the cell, it functions as a subcellular organelle, but its origins lie elsewhere. As long ago as 1890, German cell biologist Richard Altmann proposed that mitochondria were autonomous elemental life forms, similar to bacteria. In the first half of the 20th century, a number of investigators made similar links between mitochondria and bacteria. However, it was only with the discovery of mitochondrial DNA (mtDNA) in the 1960s that the idea that mitochondria were derived from bacteria gained wider acceptance, particularly in the context of the serial endosymbiotic theory that proposed that the eukaryotic cell originated from multiple prokaryotic precursors. Although some components of this theory have been abandoned (e.g. spirochaetes as precursors of eukaryotic cilia and flagella), evidence for and acceptance of the endosymbiotic origins of mitochondria have accumulated steadily over the past half century and numerous extensive and deep similarities are now recognised between mitochondria and their bacterial relatives. Most microbiologists and cell biologists are probably already aware of the fact that mitochondria are now considered descendents of endosymbiotic bacteria and they are comfortable with this description of the facts. However, the way we describe the world influences the way we think about it, so what if we abandon caution and state simply that mitochondria are bacteria and see where this reformulation leads us?
Time to recognise that mitochondria are bacteria? Trends Microbiol. Nov 29 2010
The scientific community is comfortable with recognising mitochondria as organelles that happen to be descendants of bacteria. Here, I playfully explore the arguments for and against a phylogenetic fundamentalism that states that mitochondria are bacteria and should be given their own taxonomic family, the Mitochondriaceae. I also explore the consequences of recognizing mitochondria as bacteria for our understanding of the systemic response to trauma and for the prospects of creating transgenic mitochondria.