Rare Protozoan from Sludge in Norwegian Lake Does Not Fit On Main Branches of Tree of Life

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http://www.sciencedaily.com/releases/2012/04/120426104853.htm

headline:

Rare Protozoan from Sludge in Norwegian Lake Does Not Fit On Main
Branches of Tree of Life

ScienceDaily (Apr. 26, 2012) — Humankind's remotest relative is a very
rare micro-organism from south-Norway. The discovery may provide an
insight into what life looked like on earth almost one thousand
million years ago.

Biologists all over the world have been eagerly awaiting the results
of the genetic analysis of one of the world's smallest known species,
hereafter called the protozoan, from a little lake 30 kilometer south
of Oslo in Norway.

When researchers from the University of Oslo, Norway compared its
genes with all other known species in the world, they saw that the
protozoan did not fit on any of the main branches of the tree of life.
The protozoan is not a fungus, alga, parasite, plant or animal.

"We have found an unknown branch of the tree of life that lives in
this lake. It is unique! So far we know of no other group of organisms
that descend from closer to the roots of the tree of life than this
species. It can be used as a telescope into the primordial micro-
cosmos," says an enthusiastic associate professor, Kamran Shalchian-
Tabrizi, head of the Microbial Evolution Research Group (MERG) at the
University of Oslo.

His research group studies tiny organisms hoping to find answers to
large, biological questions within ecology and evolutionary biology,
and works across such different fields as biology, genetics,
bioinformatics, molecular biology and statistics.

World's oldest creature

Life on Earth can be divided up into two main groups of species,
prokaryotes and eukaryotes. The prokaryote species, such as bacteria,
are the simplest form of living organisms on Earth. They have no
membrane inside their cell and therefore no real cell nucleus.
Eukaryote species, such as animals and humankind, plants, fungi and
algae, on the other hand do.

The family tree of the protozoan from the lake near Ås starts at the
root of the eukaryote species.

"The micro-organism is among the oldest, currently living eukaryote
organisms we know of. It evolved around one billion years ago, plus or
minus a few hundred million years. It gives us a better understanding
of what early life on Earth looked like.," Kamran says to the research
magazine Apollon.

How they move

The tree of life can be divided into organisms with one or two
flagella. Flagella are important when it comes to a cell's ability to
move. Just like all other mammals, human sperm cells have only one
flagellum. Therefore, humankind belongs to the same single flagellum
group as fungi and amoebae.

On the other hand it is believed that our distant relatives from the
family branches of plants, algae and excavates (single-celled
parasites) originally had two flagella.

The protozoan from Ås has four flagella. The family it belongs to is
somewhere between excavates, the oldest group with two flagella, and
some amoebae, which is the oldest group with only one flagellum.

"Were we to reconstruct the oldest, eukaryote cell in the world, we
believe it would resemble our species. To calculate how much our
species has changed since primordial times, we have to compare its
genes with its nearest relatives, amoebae and excavates," says
Shalchian-Tabrizi.

Caught with a tasty morsel

The protozoan is not easy to spot. It lives down in the sludge at the
bottom of a lake.

It is 30 to 50 micrometres long and can only be seen with a
microscope. When Professor Dag Klaveness of MERG wants to catch the
protozoan he sticks a pipe down into the lakebed, removes a column of
sludge and pours a bile green algae mixture over it.

The algae are such tempting morsels for the small protozoa that they
swim up.

"We can then pick them out, one by one, with a pipette," says
Klaveness.

There are not many of them. And the University of Oslo biologists have
not found them anywhere else other than in this lake.

"We are surprised. Enormous quantities of environmental samples are
taken all over the world. We have searched for the species in every
existing DNA database, but have only found a partial match with a gene
sequence in Tibet. So it is conceivable that only a few other species
exist in this family branch of the tree of life, which has survived
all the many hundreds of millions of years since the eukaryote species
appeared on Earth for the first time."

Not very sociable

The protozoan lives off algae, but the researchers still do not know
what eats the protozoan. Nor do they know anything about its life
cycle. But one thing is certain:

"They are not sociable creatures. They flourish best alone. Once they
have eaten the food, cannibalism is the order of the day," notes
Klaveness.

The protozoan has a special cell indentation. It looks like a groove.

"The species has the same intracellular structure as excavates. And it
uses the same protuberances as amoebae to catch its food. This means
that the species combines two characteristics from each family branch
of the main eukaryote groups. This further supports the hypothesis
that the species from this lake belongs to a primordial group. Perhaps
it descended from the antecedents of both the excavates and amoeba?"
asks Shalchian-Tabrizi.

The protozoan was discovered as early as 1865, but it is only now
that, thanks to very advanced genetic analyses, researchers understand
how important the species is to the history of life on Earth.

Breeding enormous quantities of the protozoan ... (cont)