Satellite image of 2011 bloom, Lake Erie

Satellite image of 2011 bloom, Lake Erie’s worst bloom in recent years, which impacted over half of the lake shore. Credit: MERIS/ESA, processed by NOAA/NOS/NCCOS

In one of the most comprehensive studies to date, University of North Carolina at Chapel Hill researchers have sequenced the genes of a harmful algal bloom, unveiling never-before-seen interactions between algae and bacteria that are thought to propagate their growth. The work also opens up the possibility of forecasting the appearance of a bloom and taking measures to prevent it.

“This technique has given us one of the most detailed looks to date into the strategy algae use to grow uncontrollably, leading to devastating consequences in our coastal communities,” said Adrian Marchetti, who led the research in UNC’s department of marine sciences. “It is also one of the first efforts to get the algae to tell us what’s going on in their natural environment, which wasn’t possible to this degree before. Now, states have the potential to be more prepared than ever to warn the public about the potential of a harmful bloom and mitigate their effects.”

A bloom in the Neuse estuary

A bloom in the Neuse estuary in North Carolina. This system is severely impacted, exhibiting both primary and secondary eutrophication symptoms. The main source of nutrients is due to effluents from pig farming in the watershed. Courtesy:

Algae can grow uncontrollably when too many nutrients overload the water system, making conditions ripe for a bloom, especially when combined with increased temperatures and a dry spell after a heavy rain.

In the past decade, harmful algal blooms have increased in every U.S. coastal state. In the U.S. alone, experts estimate that harmful algae blooms have been responsible for more than $82 million in annual economic losses due to fish kills and poor water quality that makes water undrinkable and limits recreational use. With climate change, harmful algal blooms are anticipated to rise, further affecting coastal and lake communities.

“There isn’t a way to prevent these blooms just yet, but the ability to predict them opens up that possibility, should future technologies or strategies arise that allow researchers and state officials to do so,” said Weida Gong, a graduate student who led the research with Dr. Marchetti.

The UNC researchers sequenced a harmful bloom in the Neuse River Estuary, which empties into Pamlico Sound, and compared it to algae in an area of the estuary that were not experiencing a bloom. The comparison allowed the researchers to see which genes algae (specifically the blooming dinoflagellates, the main driver of this bloom) express when growing rapidly against the genes they express under normal conditions.

They found that, when in bloom, algae ramp up the expression of genes that help facilitate the exchange of vitamins and other nutrients with bacteria, in what may be a mutually beneficial relationship. For example, the algae expressed genes that make their surfaces sticky, making it easier for the bacteria to attach and acquire nutrients from the algae and vice versa.

The exchange is also a lot more intimate than ever known to be before, such that the algae appear to produce nutrients in the form that bacteria can absorb and vice versa.

Neuse River

This is a sample from the Neuse River estuary on the North Carolina coast. Photo: Mary Lide Parker, UNC-Chapel Hill

Until now, methods to understand microbial interactions within an algae bloom have been very limited. In order to see how algae respond to increased nutrients, researchers had to take the algae out of their natural environment and test them in a lab. They would also have to test which species were present and how each was affected, a very time intensive process that still did not provide much information about how algae were interacting with other microorganisms in their environment.

With these new sequencing techniques, all the researchers have to do is sequence the microbes in the water, which tells them which species are present and how they respond.

“That’s the power of this technique,” said Hans Paerl, a distinguished professor at UNC’s Institute of Marine Sciences. “It gets the algae to tell us how they respond to changes in their natural environment – and that’s the best way for us to understand the cause and effect relationship that is going to help intervene in targeted and meaningful ways to protect our communities.”

The work appears in the Dec. 2 issue of The ISME Journal: Multidisciplinary Journal of Microbial Ecology.