Strange Cell Challenges Fundamental Assumption

Decades ago, a microbe called Monocercomonoides was discovered in the droppings of a pet chinchilla (obviously the go to source for new microbes) and what it lacks makes it the first of it kind known to science.

This little bugger seems to be the only known eukaryote (complex cells with membranes containing a nucleus and organelles) to have utterly done away with mitochondria.



ScienceNews - Gut microbe may challenge textbook on complex cells

Cataloging DNA in the microbe turns up none of the known genes for mitochondrial proteins. But stealing genetic material from bacteria — which survive without mitochondria — allowed the microbe to do without them, too, researchers report May 12 in Current Biology.

Mitochondria are tiny capsules that speckle the insides of all complex cells from pond scum to people, or so textbooks have said for decades. Some complex (or eukaryotic) cells look as if they have no mitochondria; so far, though, further searches have eventually detected mitochondrial remnants. But Monocercomonoides appears to have completely done away with mitochondria and the genes to make them, says study coauthor Anna Karnkowska, an evolutionary biologist now at the University of British Columbia in Vancouver. This discovery marks “the most extreme mitochondrial reduction observed,” says Vladimír Hampl of Charles University in Prague, also a coauthor of the study.

Although commonly described as cell powerhouses, mitochondria don’t have much to do with supplying energy for cells that live in low-oxygen or no-oxygen environments, Karnkowska says. For these anaerobic cells, mitochondria can serve as more of a building studio. One supposedly essential mitochondrial function, scientists have proposed, is assembling clusters of iron and sulfur that activate a class of widely useful cell compounds. Bacteria and other simple (prokaryotic) cells have their own assembly systems, and they don’t need to wall off the construction of iron-sulfur clusters. The newly studied Monocercomonoides carry the genes for an assembly system that looks as if it was taken from bacteria, the researchers conclude.

I'm just spit balling here but this seems to make sense if you consider the endosymbiotic hypothesis for the origins of mitochondria which holds that mitochondria were prokaryotes (think bacteria) that at some point long long long long ago, came to reside as symbionts living inside of eukaryotic cells, performing functions that their host cells couldn't do themselves.

So perhaps at some at some point, a prokaryote wound up in an ancestor of Monocercomonoides and by a mechanism like horizontal gene transfer (HGT), its genes ended up in the nuclear DNA of Monocercomonoides, allowing it to do for itself more efficiently what the mitochondria had been doing previously?

This is so exciting I cant wait to get my hands on chinchilla ***t to play with. On another note basically your saying the general idea here is that a mitocondria was basically its own organism at some point?

a reply to: Brotherman

Yes and no. The principle topic of this thread is the discovery of the first eukaryote (cells with nuclei and organelles) encountered by science that is totally devoid of mitochondria and mitochondria have been assumed to be essential. Not only is there a lack of mitochondria, there is a lack of nuclear DNA that produces proteins that are specific to mitochondria (mitochondria have their own DNA but not enough to synthesize everything they require).

In the case of Monocercomonoides, it appears that what the mitochondria might otherwise be doing is being done by the cell, which has bacteria-like if not bacteria-derived DNA in its nucleus which it uses to synthesize proteins/enzymes that are used for bacteria-like mechanisms.

I was trying to imagine how this would come to be and that's what made me refer to the prevailing hypothesis for the origins of mitochondria which is that their ancestors were ancient bacteria that first evolved outside of cells.

Further reading about the endosymbiotic origins of mitochondria:

Evolutionary Origin of Mitochondria

originally posted by: Brotherman
This is so exciting I cant wait to get my hands on chinchilla ***t to play with.

Thank you for making me spit beer all over my keyboard.

On topic, this seems like quite an interesting discovery. I'll have to read through the sources later, after I dry my keyboard off.