Plastic-eating bacteria help clean the seas

Species can tackle marine pollution if enough is grown, but it produces a lot of CO2, say researchers

THE mystery of where all the plastic goes after it is dumped in the ocean has long puzzled scientists.

At least 14 million tons of the material finds its way into marine environments each year, yet only about 1 per cent is detected in sampling surveys.

Now scientists believe they have solved at least part of the riddle – bacteria are eating it. A study by the Royal Netherlands Institute for Sea Research (NIOZ) has proved that the widespread bug bacterium Rhodococcus ruber digests plastic, turning it into carbon dioxide and other less harmful substances.

“This is the first time we have proved in this way that bacteria actually digest plastic into CO2 and other molecules,” said Maaike Goudriaan, a doctoral student at NIOZ. “This is certainly not a solution to the problem of the plastic soup in our oceans. It is, however, another part of the answer to the question of where all the ‘missing plastic’ in the oceans has gone.”

For the research, the team carried out laboratory experiments, feeding plastic to the bacteria in seawater after it had been treated with UV light to mimic the effects of the sun. Sunlight is known to break down plastic into tiny chunks which are easier for bacteria to absorb.

The team estimates that Rhodococcus ruber alone can break down at least 1 per cent of available plastic per year. Previous studies suggested that large amounts of plastic in oceans and seas fall below the surface, making it more difficult to detect but the new research shows a significant amount may be being digested by widespread bacteria.

Researchers said it could technically be possible to use the bacteria to clean up more plastic in the ocean, but warned it would require growing “stupendous amounts”. Such a scheme could also end up producing alarming amounts of carbon dioxide which would be damaging for the planet.

Rhodococcus ruber is found across the globe and is abundant in soil, water and marine environments.

The species was chosen for testing because it is known to transform a number of harmful pollutants, including industrial chemicals and pesticides, into harmless molecules. After proving this in the laboratory, the team now wants to find out whether wild bacteria also eat plastic and have started pilot experiments with sediment collected from the floor of the Wadden Sea.

“The first results of these experiments hints at plastic being degraded, even in nature,” added Ms Goudriaan. “I see it as one piece of the jigsaw, in the issue of where all the plastic that disappears into the oceans stays. If you try to trace all our waste, a lot of plastic is lost ... digestion by bacteria could possibly provide part of the explanation.”

The Dutch researchers believe sunlight is playing a major part in breaking down microplastics. They estimate that about 2 per cent of visibly floating plastic may disappear from the ocean surface in this way each year.

The research was published in the