Flemish researchers stumble upon superpower bacteria


A Dutch-Flemish team of researchers has discovered that an intriguing type of bacteria is functioning as a natural firewall in coastal areas affected by oxygen depletion

Restorative powers

Bacteria that produce electricity are helping keep marine life safe from toxic chemicals, a team of researchers has found. The team includes scientists from the Free University of Brussels (VUB), the Royal Netherlands Institute of Sea Research and Utrecht University.

The researchers have been working in Lake Grevelingen in Zeeland, the Netherlands, which used to be an offshoot of the North Sea. Coastal areas commonly see levels of oxygen in the water fall during the summer months, especially in high-population areas, where toxins – including agricultural runoff and human sewage – are pumped into the sea. Rising temperatures as a result of climate change exacerbate the problem.

At the same time as oxygen levels drop, quantities of hydrogen sulphide build up in the sediment on the bottom. Hydrogen sulphide is known to us as the rotten egg smell of stink bombs, but to marine life it’s poison.

Sometimes it breaks through the surface of the sediment, with disastrous effects for marine life. In one instance, large numbers of lobsters beached themselves rather than stay in the water when the sulphides broke through.

“Oxygen depletion happens quite a lot, but the sulphide release is less common. It happens in just one system in Zeeland,” explains professor Filip Meysman, a researcher at VUB and the Dutch sea research institute. “It’s not common in the North Sea at the moment, maybe it will be after 100 years of climate change.”

But in other waters, such as the Gulf of Mexico at the mouth of the Mississippi river, “it returns every year, as it does in the Adriatic Sea and at the coast off of Shanghai,” he says. “There are many people living in these areas, so there’s a lot of wastewater and run-off from agriculture entering the sea.”  

Lucky bacteria

The team set out to study the effects of oxygen depletion on the waters of Grevelingen, an arm of the sea north of the Zeeland island of Schouwen-Duiveland, now closed off by the Brouwersdam road connection.

“The research was designed to look into the consequences of oxygen deficiency in the water,” says Meysman. “Then we stumbled onto these electric bacteria, and now they’re the main focus of the research because they’re very intriguing and unusual.” 

It’s good to know that you’re lucky, but it is much better to know why you’re lucky

- VUB researcher Filip Meysman

Made up of a long chain of cells, these cable bacteria are about five centimetres long and one micrometre thick (or one-millionth of a metre). The bacteria feed on the iron sulphide in the sediment, which causes a transfer of electrons and the production of an electric current. 

“They love the sulphides because they are energy-rich,” explains Meysman. “The iron remains behind and becomes oxidised, and that creates a rusty layer on top of the sediment. The iron is actually a waste product of their metabolism, which then prevents the sulphide from escaping the sediment to pollute the water.”

The bacteria, the team found, colonise the area in springtime, year after year – luckily for the oyster farmers in the lake, whose beds would be devastated by any upsurge in sulphides. The existence of cable bacteria firewalls has been confirmed, the team found, in other coastal areas in the world associated with sulphide pollution.

“The ecological and fisheries impact of these sulphide cataclysms can be enormous, but, luckily, they are really exceptional,’ Meysman says. “The problem was that we didn’t really understand why these events are so rare. It’s good to know that you’re lucky, but it is much better to know why you’re lucky.”

Their study, he says, “now demonstrates that there is a natural firewall mechanism in place that delays or even prevents the escape of sulphide from sediments”.

Photo: A researcher from the Royal Netherlands Institute of Sea Research holds a water sample that contains cable bacteria
©Royal Netherlands Institute of Sea Research

Free University of Brussels (VUB)

The VUB was established as a spin-off of the French-speaking Université Libre de Bruxelles in the 1960s. It’s an internationally oriented and liberal institution, and the only Dutch-speaking university in the capital.
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