The ancestors of mitochondria

One of the more plausible theories about the origin of the mitochondria, organelles specialized in performing the cellular respiration, is the endosymbiotic theory, according to which these organelles descend from bacteria that became endosymbionts of other host cells. Probably this is also the origin of chloroplasts. Many of their characteristics confirmed this theory, for example: they contain their own DNA, their structure based on membranes is similar to that of bacteria, and many other features as ribosomes, proteines and size are similar to the bacteria's ones.

Recently, the researchers of the Oregon State University and of the University of Hawaii at Manoa have discovered the possible ancestors of mitochondria.


It is a group of bacteria known as SAR11 (class Alphaproteobacteria), which are very abundant in the ocean. The discovery was made possible by the comparison between the genomes of mitochondria of many eukaryotes and that of SAR11 bacteria, which showed an evolutionary connection.

Moreover, the hypothesis is supported by the fact that these organisms are very common in the oceans, and if also their ancestors would have been so common in this environment, this would have facilitated meetings with potential host cells. These microorganisms, as has been noted by the researchers, have a particular physiology that make them suitable to be dependent on other organisms.