'Brown Tide' Algae Exploit Coastlines

New Studyby Researchers at Columbia University Highlights Survival Skills That Have Made Aureococcus the Bane of Fishermen, Boaters and Real-estate Agents

Building on previous mapping ofAureococcus' genome, the study, published in the journal Frontiers in Microbiology this summer, confirms that the genes previously hypothesized to help Aureococcus survive in murky nutrient-rich waters, switch on in conditions typical of estuaries degraded by human activity.

While other photosynthetic algae crave sunlight, Aureococcus can live for days in the dark. When other algae run out of their preferred inorganic nutrients and die, Aureococcus is able to feast on the all-you-can-eat buffet of organic nutrients, sometimes derived from lawn fertilizers and sewage. "They are opportunists," said study lead authorKyle Frischkorn, a graduate student at Lamont-Doherty. "They can exploit the low inorganic nutrient situations that other algae can't, and they continue to grow even when high cell densities shade out light."

Their secret lies in their DNA. In sequencing Aureococcus' genome, researchers discovered it has up to three times as many light-harvesting genes as competing algae. Aureococcus also has the capacity to make enzymes that can break down organic nitrogen and phosphorus when inorganic nutrients run low. Further, its tiny stature—about the size of most bacteria--means it needs fewer resources like nitrogen and phosphorus to compete.

Brown tide usually appears after the spring diatom bloom has depleted estuaries of inorganic nutrients. Aureococcus is able to take over by using alternative organic forms of nitrogen and phosphorus and crowding out remaining competitors as it blooms and blocks out still more light. "We knew Aureococcus could survive and even thrive under adverse conditions," saidSonya Dyhrman, a microbiologist at Lamont-Doherty and a senior author on both studies. "Studying their genes allows us to understand how they are able to do this."

In the Frontiers study, researchers grew a strain of Aureococcus in the lab under conditions of low light, inorganic nitrogen and phosphorus, and also in a control environment of abundant light and inorganic nutrients. They analyzed more than 100 million fragments of RNA, which tell Aureococcus which proteins to make to exploit its environment. Sure enough, Aureococcus turned on its light-harvesting genes in murky water, and its ability to scavenge those alternative organic forms of nitrogen and phosphorus in low inorganic nutrient conditions.

The experiments also turned up a surprise. Aureococcus has developed a way to pump a toxic form of arsenic from its cells. In low-phosphorus conditions, Aureococcus inadvertently draws in arsenate, a form of naturally occurring arsenic that chemically resembles phosphate. To avoid exposure, Aureococcus reduces the arsenate to arsenite, an even more toxic form of arsenic, and pumps it from its cells into the water. The extent to which this toxic byproduct is produced during brown tides, and its effect on the environment and humans is so far unknown.

Researchers suspect that Aureococcus has always lived in the coastal environments where it now thrives. As Long Island's population has boomed, rising nutrient loads from septic systems, aging sewer plants and lawns have seeped into the groundwater, which recharges Long Island estuaries. In these degraded waters, Aureoccocus appears to be uniquely suited to exploit the low light and high organic nutrient levels. "The organism is probably more widespread than we know," said study coauthorChristopher Gobler, a marine biologist at Stony Brook University who led the earlier genome study.

The link between algae blooms and excess nutrients from sewage and fertilizers has been known for decades. Still, towns and cities have been slow to build and upgrade sewer plants, and homeowners and farmers reluctant to change growing practices. Excess manure and fertilizers spread on farms is thought to have fueled the toxic algae bloom that covered Lake Erie in green slime this summer, leaving nearly half a million people in Ohio without water for two days.

On Long Island, the main culprit producing the excess nutrients appears to be faulty septic systems. An estimated 350,000 septic systems on eastern Long Island's South Shore are considered failing, according to aJanuary reportby the Suffolk County Executive. Between 1987 and 2001, nitrogen levels in the county's groundwater (which also supplies its drinking water) jumped40 percent to 200 percentin places. More than half of the nitrogen in Great South Bay has been traced to septic tanks and cesspools, according toa recent study. Algae blooms and excess nitrogen led New York's Department of Environmental Conservation in 2008 to declare the South Shore's 60-mile long estuary impaired.

Local government has begun to act. Suffolk County Executive Steven Bellone recentlydeclarednitrogen "public enemy number one" and is lobbying New York Gov. Andrew Cuomo for state funding to offset the cost of connecting eastern Long Island to a sewage treatment plant.

Source: Columbia University

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