Biological complexity: protozoa sans mitochondria (Introduction)

by David Turell , Friday, May 13, 2016, 14:30 (2895 days ago) @ David Turell

A startling new find. A protozoa, which means a eukaryote, without mitochondria. Of course the authors insist, per Darwin, that they must have had them and modified to lose them, per common descent, but did they?:-http://www.the-scientist.com/?articles.view/articleNo/46077/title/Mysterious-Eukaryote-Missing-Mitochondria/&utm_campaign=NEWSLETTER_TS_The-Scientist-Daily_2016&utm_source=hs_email&utm_medium=email&utm_content=29555469&_hsenc=p2ANqtz--CKLrHgo8ZgM3kquTKL8rNpjpGLfmL1zHFrThZ0J1T7op9N6vsWmnOdHxnL8yBBiGZZV7B2w2ssEsFKAn_KpBnitrOew&_hsmi=29555469/-"Scientists have long thought that mitochondria—organelles responsible for energy generation—are an essential and defining feature of a eukaryotic cell. Now, researchers from Charles University in Prague and their colleagues are challenging this notion with their discovery of a eukaryotic organism, Monocercomonoides species PA203, which lacks mitochondria. The team's phylogenetic analysis, published today (May 12) in Current Biology, suggests that Monocercomonoides—which belong to the Oxymonadida group of protozoa and live in low-oxygen environments—did have mitochondria at one point, but eventually lost the organelles.-***-"This study shows that mitochondria are not so central for all lineages of living eukaryotes,” Toni Gabaldon of the Center for Genomic Regulation in Barcelona, Spain, who also was not involved in the work, wrote in an email to The Scientist. “Yet, this mitochondrial-devoid, single-cell eukaryote is as complex as other eukaryotic cells in almost any other aspect of cellular complexity.”-***-"Hampl decided to sequence the genome of Monocercomonoides, a little-studied protist that lives in the digestive tracts of vertebrates. The 75-megabase genome—the first of an oxymonad—did not contain any conserved genes found on mitochondrial genomes of other eukaryotes, the researchers found. It also did not contain any nuclear genes associated with mitochondrial functions.-***-"Some anaerobic protists, for example, have only pared down versions of mitochondria, such as hydrogenosomes and mitosomes, which lack a mitochondrial genome. But these mitochondrion-like organelles perform essential functions of the iron-sulfur cluster assembly pathway, which is known to be conserved in virtually all eukaryotic organisms studied to date.-"Yet, in their analysis, the researchers found no evidence of the presence of any components of this mitochondrial pathway.-"To form the essential iron-sulfur clusters, the team discovered that Monocercomonoides use a sulfur mobilization system found in the cytosol, and that an ancestor of the organism acquired this system by lateral gene transfer from bacteria. This cytosolic, compensating system allowed Monocercomonoides to lose the otherwise essential iron-sulfur cluster-forming pathway in the mitochondrion, the team proposed.-“'This work shows the great evolutionary plasticity of the eukaryotic cell,” said Karnkowska, who participated in the study while she was a postdoc at Charles University. Karnkowska, who is now a visiting researcher at the University of British Columbia in Canada, added: “This is a striking example of how far the evolution of a eukaryotic cell can go that was beyond our expectations.”-“'The results highlight how many surprises may await us in the poorly studied eukaryotic phyla that live in under-explored environments,” Gabaldon said.-"Ettema agreed. “Now that we've found one, we need to look at the bigger picture and see if there are other examples of eukaryotes that have lost their mitochondria, to understand how adaptable eukaryotes are.'”-Comment: I like the phrase 'evolutionary plasticity' It fits my contention that a 'drive to complexity' is all that is needed to advance evolution and explain to dhw all the weird parts of the bush of life. Invent novelty, however complex, and what survives becomes the evolutionary advance (per Darwin). Perhaps learning to live on sulfur, not oxygen, negated the need for mitochondria which are generally the oxygen-burning organelles.