First eukaryotes found without a normal cellular power supply

You can’t survive without mitochondria, the organelles that power most human cells. Nor, researchers thought, can any other eukaryotes—the group of organisms we belong to along with other animals, plants, fungi, and various microscopic creatures. But a new study has identified the first eukaryote that has ditched its mitochondria, suggesting that our branch on the tree of life may be more versatile than researchers thought.

“This is a discovery of fundamental importance,” says evolutionary biologist Eugene Koonin of the National Center for Biotechnology Information in Bethesda, Maryland, who wasn’t connected to the study. “We now know that eukaryotes can live happily without any remnant of the mitochondria.”

Mitochondria are the descendants of bacteria that settled down inside primordial eukaryotic cells, eventually becoming the power plants for their new hosts. Although mitochondria are a signature feature of eukaryotes, scientists have long wondered whether some of them might have gotten rid of the organelles. The diarrhea-causing microbe Giardia intestinalis for a time seemed mitochondria-free, but on closer investigation, it and other suspects proved to be false alarms, containing shrunken versions of the organelles.