Marine algae can digest plastic with help from a bacterial enzyme
The effort to clean the ocean might get a little help. A bacterial enzyme allows microalgae to degrade plastic litter in saline waters.
Cell biologists from Marburg, Germany, discovered this potential when they added the enzyme PETase to marine diatoms. The enzyme originated from a bacterium that uses PETase to degrade synthetic polymers. The findings by Dr. Daniel Moog and his team were published in “Microbial Cell Factories”.
The polymer PET is commonly used for plastic bottles. Estimates put the yearly production of this material in 2020 at approximately 70 million tons. After single-use, the products then end up as trash, of which a major part ends up in the environment, mainly the oceans. Daniel Moog describes the severity of plastic littering in the environment: “According to some estimations, by the year 2050, there will be more plastic than fish in our seas. This plastic litter can be taken up by organisms and may potentially harm them, for instance due to toxic additives embedded in the polymers.”
It has already been known that some bacteria can degrade the polymer PET – microorganisms such as Ideonella sakaiensis produce an enzyme called PETase, which splits the long chain molecules of synthetic polymers into its base parts. “This is highly interesting for degradation of small particles such as microplastics”, Moog explains. “Microplastics is otherwise hard to remove from seas, where a lot of plastic accumulates.” However, Ideonella is not adapted for life in saline environments such as the world’s seas. “That is why this bacterium is not suited for biological remediation of the polluted oceans.”
As a consequence, the research group decided to use the marine diatom Phaeodactylum tricornutum. They transferred a tailormade version of the bacterial gene into the diatom to produce the required enzyme.
They subsequently tested whether the produced enzyme actually degrades PET and an additional polymer similar to it. For this, the diatoms were cultured in vessels containing small ground plastic particles. Testing revealed that the particles hat grooves and holes when exposed to the enzyme secreted from the diatoms. In the end, only harmless degradation products were left over.
“The PETase-producing diatoms may contribute to a climate-friendly recycling of PET”, Moog says. He envisions spatially limited plants similar to waste water treatment plants in which the modified diatom could degrade the ocean’s microplastic. “Tests showed that our approach could remove PET from saltwater in laboratory testings”, the biologist says. The biological plastic degradation process now needs to be optimized in such a way that it becomes technically feasible and efficient.
Source (German): https://www.chemie.de/news/1163428/meeresalgen-verdauen-plastik-mittels-bakterienenzym.html
Original article: Daniel Moog & al.; "Using a marine microalga as a chassis for polyethylene terephthalate (PET) degradation"; Microb. Cell Fact.; 2019