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Researchers Sequence Algal Species Involved in Brown Tides

By a GenomeWeb staff reporter

NEW YORK (GenomeWeb News) – Harmful algal blooms that kill sea life and impact fisheries involve at least one algal species with a genetic propensity to flourish in conditions produced by human activity, according to a genome sequencing paper set to appear online this week in the Proceedings of the National Academy of Sciences.

Researchers from the US and Australia used a combination of genome sequencing and metaproteomics to characterize the genome of the brown phytoplankton Aureococcus anophagefferens and compare it with competing phytoplankton. Their findings indicate that the newly sequenced species is particularly suited to conditions that coincide with the brown tides in which it's found.

"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," co-corresponding author Christopher Gobler, a researcher at Stony Brook University, 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."

"It's a great resource for our community," US National Office for Harmful Algal Blooms Director and Woods Hole Oceanographic Institution researcher Don Anderson, who was not involved in the current study, said in a statement, "[T]he more we learn about Aureococcus, the easier it's going to be to learn about the other [harmful algal bloom] species."

Aureococcus is a component of a type of harmful algal bloom, or HAB, known as brown tides, which occur on the Eastern US coast and off the coast of South Africa. These blooms, which are poisonous to shellfish and other sea life, usually occur in relatively shallow water containing high levels of nitrogen and organic carbon material and low levels of inorganic nutrients and light.

Such conditions sometimes arise naturally, researchers noted, but are more likely to occur in the presence of fertilizer runoff and pollution caused by other human activities.

"The frequency and impact of HABs have intensified in recent decades," Gobler and co-authors wrote, "and anthropogenic processes, including eutrophication, have been implicated in this expansion."

For the current study, collaborators at the US Department of Energy's Joint Genome Institute used the Sanger approach to sequence the 56 million base genome of an A. anophagefferens isolate collected off of Long Island.

The team also did metaproteomics using 2D nano-liquid chromatography tandem mass spectrometry to get clues about the sorts of phytoplankton species that compete with A. anophagefferens during brown tides.

Among the phytoplankton detected were six species that have already been sequenced, they noted, allowing for comparisons between the genomes.

For instance, the researchers found that A. anophagefferens has a larger genome than expected for its diminutive cell size. With a predicted protein-coding gene repertoire of about 11,500 genes, they added, it also contains more genes overall than the other six phytoplankton species assessed.

This includes a preponderance of genes involved in light harvesting, organic carbon and nitrogen metabolism, detoxification, and defense against microbes and other possible predators, the team explained. Moreover, they found, the brown alga's genome contains numerous genes coding for enzymes that rely on metals and selenium.

Together, they explained, the results suggest that genes that are unique to — or enriched in — A. anophagefferens "are involved in biochemical pathways related to the environmental conditions prevailing during brown tides and thus, are likely to facilitate the dominance of this alga during chronic blooms that plague estuarine waters."

Those involved in the new study say their findings also underscore the risks associated with creating environmental conditions that favor the growth of A. anophagefferens and other HAB-associated phytoplankton.

"We now know this organism is genetically predisposed to exploit certain characteristics of coastal ecosystems," Gobler cautioned. "We also know the characteristics are there because of activities of man."

"If we continue to increase, for example, organic matter in coastal waters, then it's going to continue to favor brown tides since it's genetically predisposed to thrive in these conditions," he said.

Down the road, the team reportedly plans to incorporate RNA level information on A. anophagefferens in an effort to learn more about its gene expression under various environmental conditions.

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

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