科学美国人60秒:Microbe Breaks the Powerhouse Rules

If you were searching for a lifeform unlike anything known to science, where would you look? Scientists at Charles University, in Prague, looked in the poop of a pet chinchilla. "They were isolating a lot of various strains from various environments—including their own pets." Anna Karnkowska, an evolutionary biologist who collaborated on the work, who is now at the University of British Columbia. "Scientists like to isolate things from everywhere possible." 

They found a relative of the parasite Giardia, called Monocercomonoides. It’s eukaryotic, meaning it has organelles and a nucleus enveloping its DNA. Just like our cells, or the ones in plants, or fungi. But unlike bacteria, which don’t have those things. 

And upon closer examination, the new critter was different from every other eukaryote known to science. Because it’s missing a key organelle—it seems to have no mitochondria.

You probably learned in biology class that mitochondria, let’s all say it together, are the powerhouses of the cell. They charge up energy-rich molecules, when oxygen's around. But they do other stuff too: like manufacture certain essential proteins. This newly discovered microbe, and others that live in low-oxygen environments, use different, oxygen-free pathways to make energy. But they usually still have mitochondria for that protein assembly job. The new bug apparently pulls off the protein-synthesis by using a system that it picked up from bacteria, in what’s known as a lateral gene transfer. The findings are in the journal Current Biology. [Anna Karnkowska et al, A Eukaryote without a Mitochondrial Organelle]

Karnkowska says the microbe's ancestors probably had mitochondria at some point—then lost them once they’d acquired the bacterial system. And she says other microbes might share a similar story. "We know now that probably there are more of these weird things." And as this study suggests, they could be found in some weird places.

—Christopher Intagliata