A marine parasite’s mitochondria lack DNA but still churn out energy

One parasite that feeds on algae is so voracious that it even stole its own mitochondria’s DNA.

Mitochondria — the energy-generating parts of cells — of the parasitic plankton Amoebophyra ceratii seem to have transferred all of their DNA to the cell’s nucleus, researchers report April 24 in Science Advances. The discovery is the first time that scientists have found an oxygen-using organism with fully functional mitochondria that don’t have any mitochondrial DNA. (Some anaerobic organisms, which don’t need oxygen, and thus mitochondria, to survive, have also lost mitochondrial DNA.)

Mitochondria are thought to be bacteria that were captured by other cells and eventually became standard parts of eukaryotic cells — cells that encase their DNA and other parts in membranes. Mitochondria reside outside of the nucleus in a cell’s jellylike guts, the cytoplasm. Part of the settling-in process involved relocating some genes needed for mitochondria’s function to the nucleus of host cells. But most mitochondria kept at least a few genes. (Human mitochondria held on to 37 genes.)

Not so for A. ceratii, Uwe John of the Alfred Wegener Institute in Bremerhaven, Germany, and colleagues discovered. The parasite, which infects algae that can cause toxic blooms, has two mitochondria during the free-living stage of its life cycle. Both are able to produce energy, the researchers found. But the team couldn’t spot any DNA inside the mitochondria.

A search of the DNA in the organism’s nucleus turned up genes needed for mitochondrial function there. The scientists conclude that all of the genes necessary to make working mitochondria were transferred to the nucleus, making it possible for the tiny energy factories to keep producing energy after they lost their DNA.