Bacteria responsible for lost ocean plastic

The 'plastic paradox' may be in part down to bacteria breaking down certain polymers...
27 January 2023

Interview with 

Maaike Goudriaan, Royal Netherlands Institute for Sea Research


a photo of a plastic cup in the surf


Since 2005, marine biologists have had a problem to solve. When taking samples from the ocean, they find they are finding a lot less plastic than they would expect given the amount being dumped into the sea every year. Over the past decade and a half, a few explanations have arisen for this “plastic paradox”. Some plastics sink and end up buried at the bottom, unmeasured. UV light from the sun also contributes to the break up of some polymer chains, accounting for another chunk of the plastic deficit. But a significant proportion might also be being digested by bacteria. Maaike Goudriaan at the Royal Netherlands Institute for Sea Research has been studying the bacterium Rhodococcus ruber, which appears to be able to break down about 1% of the available plastic per year…

Maaike - We used a plastic that has specific labeled carbon isotopes, so-called carbon 13. So because these carbon atoms in the plastic are labeled, we can follow these labeled carbons. So from that, we knew that the bacterium was able to convert the polymer all the way into CO2, which is the final step in the degradation. This is the smallest part they would typically make out of plastics. And then also the labeled carbon, we found it back in the bacterial cells. The fact that we found it there means that they have actually eaten it and use it as a resource to grow.

James - So you're able to prove in the laboratory that this is what was going on, that this bacteria is able to take the plastic. So the question then becomes whether this could be a real solution to the problem of plastic pollution. Could we just colonize the sea with as many of these bacterias as we can possibly produce?

Maaike - Well unfortunately not. I mean, I get this question quite often and it would be very nice. Unfortunately. I can imagine this might be hard to picture. The oceans are very, very vast. There's a lot of currents we can't influence, and we would be talking about huge amounts of bacteria we would need to grow. So personally I would also see a large logistics problem.

James - Fair enough. But how can we use this information? The characteristics of the Rhodococcus ruber?

Maaike - Our main goal was to develop this new method to measure plastic degradation. And the reason we wanted to do that is that typically in marine environments, if plastic disappears, it seems to be very, very slow. And you can imagine that if degradation goes very slow, it might be difficult to accurately measure a difference in weight. And indeed what we also found is that Rhodococcus ruber is able to break down the polyethylene, so the plastic that we use, with a rate of 1% per year. So that's not a lot. We now know that this method works and that it can be used to measure very small degradation rates. So in that way, in the future, we would like to take samples from water column samples and also sediment samples from the sea and methods to investigate how fast plastic disappears under microbes. And with that, we hope to solve the puzzle of where the plastic goes a little bit further.


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