Living in Hell
Wednesday, July 15, 2015
In the movie Alien, the title character is an extraterrestrial creature that can
survive brutal heat and fend off toxins.
In real life, organisms with similar traits exist, such as the “extremophile” red
alga Galdieria sulphuraria.
In hot springs in Yellowstone National Park, Galdieria uses energy from the sun to
produce sugars through photosynthesis.
In the darkness of old mineshafts, in drainage as caustic as battery acid, it feeds
on bacteria and survives high concentrations of arsenic and heavy metals.
How has a one-celled alga acquired such flexibility and resilience?
To answer this question, an international research team led by Gerald Schönknecht
of Oklahoma State University and Andreas Weber and Martin Lercher of Heinrich-Heine
Universitat (Heinrich-Heine University) in Dusseldorf, Germany, decoded genetic information
in Galdieria.
They are three of 18 co-authors of a paper published in Science.
The scientists found that the Galdieria genome shows clear signs of borrowing genes
from its neighbors. Many genes that contribute to Galdieria’s adaptations were not
inherited from its ancestor red algae but were acquired from bacteria or archaebacteria.
This “horizontal gene transfer” is typical for the evolution of bacteria, researchers
say.
However, Galdieria is the first known organism with a nucleus (called a eukaryote)
that has adapted to extreme environments based on horizontal gene transfer.
“The age of comparative genome sequencing began only slightly more than a decade
ago and revealed a new mechanism of evolution — horizontal gene transfer — that would
not have been discovered any other way,” says Matt Kane, program director in the National
Science Foundation’s Division of Environmental Biology, which funded the research.
“This finding extends our understanding of the role that this mechanism plays in evolution
to eukaryotic microorganisms.”
Galdieria heat tolerance seems to come from genes that exist in hundreds of copies
in its genome, all descending from a single gene copied millions of years ago from
an archaebacterium.
“The results give us new insights into evolution,”Schönknecht says. “Before this,
there was not much indication that eukaryotes acquire genes from bacteria.”
The alga owes its ability to survive the toxic effects of such elements as mercury
and arsenic to transport proteins and enzymes that originated in genes it swiped from
bacteria.
It also copied genes offering tolerance to high salt concentrations and ones with
an ability to make use of a wide variety of food sources. The genes were copied from
bacteria that live in the same extreme environment as Galdieria.
“Why reinvent the wheel if you can copy it from your neighbor?” asks Lercher. “It
is usually assumed that organisms with a nucleus cannot copy genes from different
species — that’s why eukaryotes depend on sex to recombine their genomes. How has
Galdieria managed to overcome this limitation? It is an exciting question.”
What Galdieria did is “a dream come true for biotechnology,” says Weber. “Galdieria
has acquired genes with interesting properties from different organisms, integrated
them into a functional network and developed unique properties and adaptations.”
Future genetic engineering may allow other algae to make use of the proteins that
offer stress tolerance to Galdieria.
Such a development would be relevant to biofuel production, says Schönknecht, as
oilproducing algae don’t yet have the ability to withstand the same extreme conditions
that Galdieria does.
Story By Matt Elliott