Algae steals genes to survive toxic environment

Posted by Kate Taylor

A species of algae that can cope with 'battery acid' conditions managed it by copying genes from bacteria.

Galdieria sulphuraria lives in hot springs in Yellowstone National Park, where it uses energy from the sun to produce sugars through photosynthesis. In conditions as caustic as battery acid, it feeds on bacteria and survives high concentrations of arsenic and heavy metals.

To find out how it manages this, an international research team decoded genetic information in Galdieria - and found that its 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 common in the evolution of bacteria.
However, Galdieria is the first known eukaryote - or organism with a nucleus - to have adapted to extreme environments through 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 (NSF) Division of Environmental Biology.

"This finding extends our understanding of the role that this mechanism plays in evolution to eukaryotic microorganisms."

Galdieria's heat tolerance seems to come from genes that exist in hundreds of copies in its genome, all descending from a single gene the alga copied millions of years ago from an archaebacterium.

It's able to survive the toxic effects of such elements as mercury and arsenic thanks to transport proteins and enzymes from genes it swiped from bacteria. It also copied genes offering tolerance to high salt concentrations, and 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.

"It's usually assumed that organisms with a nucleus cannot copy genes from different species - that's why eukaryotes depend on sex to recombine their genomes," says Martin Lercher of Heinrich-Heine University in Dusseldorf.

"How has Galdieria managed to overcome this limitation? It's an exciting question."