Not only dinosaurs, but also marine phytoplankton and terrestrial plants were deposited and metamorphosed over time into oil. Some of that oil has been made into plastic that eventually made its way into the ocean. The basic chemical building blocks of plastic are well-known in nature, but anthropogenic long chain polymers are extremely difficult for natural living beings and their digestive helpers called enzymes to digest it properly. So now, we have a lot of plastics in the ocean but not enough little helpers to get rid of it naturally.
So how do we get an efficient plastic degrading enzyme faster? One idea is to go to very polluted areas around the world and see if, in the litter, some life forms have already adapted to using plastics as a new food source. For example, in the sea, space in form of a place to sit on and float around the ocean is scarce and plastic litter is perfect in that regard. So, a lot of microorganisms use the litter in their favor and start to live on it. At the same time food in form of carbon sources is limited, so the bacteria colonizing the plastic might also adapt it to eat the plastic they are living on by evolving their already existing natural repertoire of digestive helpers called enzymes.
On this journey, we try to recover these bacteria and their enzyme and access them for biotechnological application. Especially under the extreme conditions of the Deep Sea, enzymes might have evolved directly suitable for such applications. To gain plastic particles colonized by microbes, we used the neuston catamaran to collect floating plastics pieces (Figure 1) and the box core (Figure 2 & 3) to collect plastic pieces from the bottom of the ocean.
From the microplastic-enriched sediment (Figure 4) as well as from these plastic pieces (Figure 5 ) we will try to grow some of the bacteria in the lab and investigate if they have already adapted to digest plastic. The next step would be to find out which genes encode for the DNA, isolating these genes and use the pure enzyme in further tests. As it is likely that most of the bacteria will not grow under lab conditions, we will furthermore isolate the DNA directly from sediment samples to recover and safe the blueprints of the enzymes of those bacteria.
These enzymes may then be engineered by means of so-called directed evolution to work even faster and more efficient on plastic and might then be used in wastewater treatment all around the world to stop more plastics in form of microplastic to enter the oceans.
by Rebecka Molitor who is part of the PLASTISEA project – Heinrich-Heine University Düsseldorf, Germany.