CAS CONNECT 2013

30 I n 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 mine- shafts, in drainage as caus- tic as battery acid, it feeds on bacteria and survives high concentrations of arsenic and heavy metals. OSU professor leads team researching extremely resistant algae Living in Hell 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 trans- fer” 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 hori- zontal gene transfer. “The age of comparative genome sequencing began only slightly more than a decade ago and revealed a new mech- anism of evolution — horizon- tal 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 eukary- otic microorganisms.” Galdieria heat tolerance seems to come from genes that exist in hundreds of copies in its genome, all descend- ing 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 indi- cation 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 origi- nated in genes it swiped from bacteria. It also copied genes offer- ing 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 organ- isms with a nucleus cannot copy genes from different species — that’s why eukary- otes depend on sex to recom- bine their genomes. How has Galdieria managed to over- come this limitation? It is an exciting question.” What Galdieria did is “a dream come true for biotech- nology,” says Weber. “ Galdieria has acquired genes with interesting prop- erties from different organ- isms, integrated them into a functional network and devel- oped unique properties and adaptations.” Future genetic engineer- ing may allow other algae to make use of the proteins that offer stress tolerance to Galdieria . Such a development would be relevant to biofuel produc- tion, says Schönknecht, as oil- producing algae don’t yet have the ability to withstand the same extreme conditions that Galdieria does. Matt Elliott How has a one-celled alga acquired such flexibility and resilience? To answer this ques- tion, 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 andreas p.m. weber / university of dusseldorf