Mitochondria are membrane-bound components within cells that are often described as the cells’ powerhouses. They’ve long been considered as essential components for life in eukaryotes, the group including plants, fungi, animals, and unicellular protists, if for no other reason than that every known eukaryote had them. But researchers reporting in the Cell Press journal Current Biology on May 12, 2016 now challenge this notion. They’ve discovered a eukaryote that contains absolutely no trace of mitochondria at all.
“In low-oxygen environments, eukaryotes often possess a reduced form of the mitochondrion, but it was believed that some of the mitochondrial functions are so essential that these organelles are indispensable for their life,” says Anna Karnkowska, a former post-doctoral fellow at Charles University in Prague who is now at the University of British Columbia in Vancouver, Canada. “We have characterized a eukaryotic microbe which indeed possesses no mitochondrion at all.”
Organisms from the genus Monocercomonoides have been recognized for more than 80 years. They are related to the human pathogens Giardia and Trichomonas, all of which belong to a group known as Metamonada, which lives exclusively in low-oxygen environments.
In the new study, Karnkowska and Vladimir Hampl at Charles University in Prague and BIOCEV, along with colleagues from the Czech Republic and Canada, sequenced the Monocercomonoides genome. They were surprised to find that this organism lacks all mitochondrial proteins.
Monocercomonoides seems to have gotten by without mitochondria thanks to a cytosolic sulfur mobilization system (SUF) that they acquired from bacteria and that appears to substitute for essential mitochondrial functions. Through a unique combination of events including the loss of many mitochondrial functions and the acquisition of this essential machinery from prokaryotes, “this organism has evolved beyond the known limits that biologists circumscribed,” Karnkowska says. Source: Surprise! This eukaryote completely lacks mitochondria