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.
For the new study, a team led by evolutionary biologist Anna
Karnkowska, a postdoc, and her adviser, Vladimir Hampl, of Charles
University in Prague, checked another candidate, a species in the genus
Monocercomonoides.
The single-celled organism came from the guts of a chinchilla that
belonged to one of the lab members. The team decided to test it because
it belonged to a group of microbes that scientists posited had lost
their mitochondria.
When the researchers sequenced
Monocercomonoides’s genome,
they found no signs of mitochondrial genes (the organelles carry their
own DNA). Digging deeper, they determined that it
lacks all of the key proteins that enable mitochondria to function.
“The definition of eukaryotic cells is that they have mitochondria,”
says Karnkowska, who is now at the University of British
Columbia, Vancouver, in Canada. “We overturn this definition.”
Monocercomonoides may not need mitochondria because of where
it lives—in the intestines of chinchilla hosts, which it doesn’t appear
to harm. Nutrients are abundant there, but oxygen, which mitochondria
require to produce energy, is scarce. Instead of relying on
mitochondria, the organism likely uses enzymes in its cytoplasm to break
down food and furnish energy, the authors suggest. But energy
production is not the only problem that
Monocercomonoides solved............................
http://www.sciencemag.org/news/2016/05/first-eukaryotes-found-without-normal-cellular-power-supply
