February 21, 2011

Scientists Sequence Genome Of Harmful Algal Bloom Species

For the first time, researchers have sequenced the genome of a harmful algal bloom species.

Researchers found that Aureococcus' unique gene complement allows it to outcompete other marine phytoplankton and thrive in human-modified ecosystems, which could help explain the global increases in harmful algal blooms.

The brown tides caused by Aureococcus do not produce toxins that poison humans, but the long-lasting blooms are toxic to bivalves and have decimated sea grass beds leading to billions of dollars in economic losses, according to the researchers.

The blooms are annual events in estuaries along the heavily populated coastlines of the eastern U.S. and South Africa. 

The 56-million base pair Aureococcus genome was sequenced in 2007 by the Department of Energy's Joint Genome Institute from a culture isolated from the shores of Long Island, N.Y.

Members of the Aureococcus Genome Consortium were compared with the genome of other phytoplankton inhabiting the estuaries where Aureococcus blooms. 

The team found that Aureococcus shows genome-encoded advantages over its competitors and is genetically predisposed to exploit certain characteristics of human-modified coastal ecosystem.

"There are things it can do that the other algae can't, and those advantages are encoded at the genome level," said Sonya Dyhrman, a biologist at the Woods Hole Oceanographic Institution (WHOI), said in a statement. "For example, it's well-adapted to low light conditions and can survive for long periods in no light. Aureococcus had 62 light-harvesting genes whereas its competitors had, on average, a couple of dozen."

The photosynthetic microalga also shows advantages when it comes to metabolizing organic matter and handling what would normally be toxic amounts of metals. 

"When we looked at the coastal ecosystems where we find Aureococcus blooms, we found they were enriched in organic matter, were very turbid and enriched in trace metals," Christopher Gobler of Stony Brook University's School of Marine and Atmospheric Sciences and leader of the research, said in a statement. "And when we looked at the genome of Aureococcus, it ended up being enriched in genes to take advantage of these conditions. The surprise was the concordance between the genome and the ecosystem where it's blooming."

New advances in the field of genomics allowed the team to better address difficult questions in environmental biology.

Gobler said this new "ecogenomic" approach was a particularly powerful tool for understanding the dominance of different harmful algal blooms within different ecosystems around the world.

"It's really exciting to be able to apply these new tools and a molecular approach to old questions about how organisms are functioning and interacting with their environment," Dyhrman said in a press release. "I've been interested in these kinds of questions since graduate school, but we simply did not have the tools then to approach it in this way. We now have a huge new tool kit and are able to look at these questions in a much more specific way than ever before."

"I think this paper says it all," added Don Anderson, Director of the U.S. National Office for Harmful Algal Blooms and a senior scientist at WHOI. "Here's a species that blooms and for years people have been trying to understand why it blooms, when it blooms, how it is able to do that when there are so many other competing species in the water with it. With this new genomic data you have a new approach."

The researchers are planning to start looking at Aureococcus' RNA and try and determine when and how different genes are expressed throughout the lifetime of the bloom.

"By looking at when the genes are transcribed through the bloom, we're hoping to provide the next piece in the puzzle"”understanding how the genes are responding to the environment and what is fueling and causing the demise of blooms," Dyhrman, who was co-author of the study, said in a statement.

Results of the study were published in the February 21 edition of the Proceedings of the National Academy of Sciences.


Image 1: This is an aerial view of Great South Bay, N.Y., during a brown tide bloom in June 2008. Billions of A. anophagefferens cells per liter crowded into the coastline and turned the water brown. Credit: Suffolk County Department of Health Services

Image 2: These are the Aureococcus anophagefferens cells of a harmful algal bloom brown tide. Credit: Chris Gobler, Stony Brook University


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