Scientists find way to stop algae poisoning China’s dirtiest freshwater lake

• Lake Chao is ranked bottom by the central government for water quality
• Discovery of virus could allow algae to be controlled

Scientists working at China's most polluted freshwater lake have discovered a virus that could be used to tame the algae that poisons it each year.

Lake Chao, in Anhui province in the country's southeast, lies at the very bottom of the central government's rankings for water quality, partly because of algae outbreaks there. But researchers from the University of Science and Technology of China have found a previously unknown algae-eating virus that could combat the outbreaks.

Named Mic1, the virus has an oversized head and elongated tail, a body structure resembling human sperm. It can infect, suppress or kill blue-green algae, the most abundant photosynthetic micro-organism on Earth, according to the researchers' paper in the latest issue of the journal Structure.

Using the tail as an anchor, the virus can inject its DNA into a blue-green algae cell with relative ease. The virus will then multiply before tearing the host apart and moving on to other cells.

But despite the virus' presence in Lake Chao " the fifth largest lake in China " an algae bloom nearly every summer kills fish, poisons drinking water and produces a pungent smell familiar to the millions of people living nearby.

Dr Jiang Yongliang, a life scientist at the Hefei National Laboratory for Physical Sciences at the Microscale, who took part in the study, said the growth of blue-green algae in Lake Chao had outpaced the spread of the virus.

Lake Chao is known as a dumping ground for waste water, and pollutants have provided excessive nutrition for bacteria. At warm times of the year, more algae cells are created than are killed by the virus. But Mic1 can be artificially bred and released into the environment to reduce the algae bloom, according to Jiang " up to a point.

"It can only infect two known types of cyanobacterial (blue-green algae) strains," Jiang said.

The researchers are considering modifying the virus' genes so that it can infect a wider range of hosts. This is possible because the researchers have used a cryogenic electron microscope to obtain a complete picture of its structure with near-atomic resolution.

There are a few other viruses capable of killing freshwater algae, but Mic1 is the only one whose detailed structure is known.

The question remains of whether it is safe to create an algae-killing virus and set it loose. Blue-green algae, some scientists believe, gave rise to all complex life forms as the earliest oxygen-producing organism on Earth. These single-cell organisms may have triggered the Great Oxidation Event that resulted in a permanently oxygenated atmosphere around 2.4 billion years ago.

Jiang said he and his colleagues had no intention to wipe out the planet's most abundant and longest living oxygen producer.

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"We can only target a few species of the blue-green algae," he said. "When they are suppressed, other species will thrive. Some will also develop immunity to the infection. It is impossible to kill them all."

The researchers spent more than two years finding the virus, and it could take them longer to develop a commercial variant. "There is still a long way from laboratory to real-life application," Jiang said.

Cao Xihua, a researcher in marine ecology and environmental sciences at the Chinese Academy of Sciences in Qingdao, said algae bloom had become a serious environmental threat in many places around the world and scientists were exploring various methods to reduce the damage.

He said other methods included physical removal and chemical sprays, but each came with its own environmental impact, such as killing other water creatures.

"Using a virus is a biological approach and one of the possible approaches," Cao said. "The new discovery is very useful.

"But the success of a technology is affected by many factors, such as cost. It will also need to go through stringent environmental evaluations before any mass application."

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