The world has a huge plastic problem that is not yet solved. We are trying to reduce our dependence on plastic, but this is seemingly impossible in modern society. The material is too important to our daily lives despite its impact on the environment. Plastic also directly harms living organisms, as microplastics are regularly found in them. This includes the human body, with new research showing that microplastics can end up in all sorts of organs.
One way to reduce the impact of plastic waste on the environment is to develop better methods to break it down. One such idea for biodegradable plastic comes from a team of researchers at the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences.
Scientists managed to create a kind of living plastic that contains bacterial spores. While the containers are in use, the spores are inactive, but when the material needs to be disposed of, the bacteria can be activated so that they wake up and start consuming the plastic.
Bacteria lie dormant in spore form, allowing them to survive the harshest environmental conditions. When the environment is favorable, the bacteria become active again. That’s one piece of the puzzle. Bacterial spores can survive the process of creating living plastic. The other challenge is selecting the type of bacteria that will happily eat plastic when they are active.
The researchers from the Chinese Academy of Sciences developed plastic products that contained bacterial spores that would eventually destroy the plastic. They chose a form of Bacillus subtilis Bacteria that were engineered to secrete an enzyme that can break down plastic, Lipase BC. They took the enzyme from another bacterium, Burkholderia cepacia.
When exposed to heavy metal ions, the bacteria turned into spores. Prof. Zhuojun Dai’s team combined the spores with PCL (polycaprolactone) plastic beads. They melted the mixture and formed solid pieces of plastic. The bacteria were not harmed and the plastic looked and behaved like normal plastic. The “living plastic” was not alive at all as long as the bacteria remained in spore form.
The researchers developed two methods to activate the microorganisms. One of them is to expose the plastic to an enzyme. This awakens the bacteria, which then consume the plastic. The bacteria take 6-7 days to dispose of a container.
Another option is to compost the plastic. Destroying the containers also activated the bacteria. In this scenario, the bacteria needed 25 to 30 days to decompose the plastic after it was buried in the soil. Regular PCL takes 55 days to degrade to a level that is no longer visible to the human eye.
To test the viability of the bacteria-laden plastic, the team submerged the living plastic in gasoline for two months. The PCL container retained its shape, proving that it functions like a regular plastic container until exposed to the right conditions that activate the bacteria.
The researchers also investigated the possibility of mixing the plastic-eating spores with other plastics. They were able to mix spores of a bacterium carrying green fluorescent plasmids with different types of plastics: PBS (polybutylene succinate), PBAT (polybutylene adipate-co-terephthalate), PLA (polylactic acid), PHA (polyhydroxyalkanoates) and even PET (polyethylene terephthalate).
They released the spores by physically grinding them and found that the bacteria were activated and released the fluorescent protein. This experiment shows that there is scope for using similar technologies to create other types of biodegradable plastics in the future. The bacteria survive manufacturing processes that involve temperatures of up to 300 °C (572 °F).
This is not the only research on this topic. New Atlas points out that a team at UC San Diego has developed TPU (thermoplastic polyurethane) that contains spores. This plastic begins to decompose when it is discarded in a landfill.
The study by the Chinese Academy of Sciences is now available in Nature Chemical Biology.
