When the going gets tough for certain bacteria, they form into spores that can withstand the harshest of environments. Scientists have now utilized that fact to produce "living plastic" that biodegrades – but only under specific conditions.
Spores are a dormant form taken by some types of bacteria, typically when nutrients are in short supply.
They are protected by a tough outer coating that allows them to survive high temperatures, high pressure, desiccation, and caustic chemicals. This makes them one of the most resistant of all life forms. They are able to remain in an inactive state for years or even centuries at a time, becoming active again only when triggered by the right environmental cues.
Some bacteria are also known to break down plastic waste, keeping it from persisting in the environment. Scientists from the Chinese Academy of Sciences have now taken spores of such bacteria and embedded them in solid plastic, which remains tough and intact until the spores are revived.
Led by Prof. Zhuojun Dai, the researchers created a form of Bacillus subtilis bacteria that was genetically engineered to secrete a plastic-degrading enzyme known as lipase BC. Upon being stressed by exposure to heavy metal ions, these microbes formed into spores. Those spores were then mixed with beads of PCL (polycaprolactone) plastic, after which the mixture was melted and extruded to form pieces of solid plastic.
Tests showed that the resulting "living plastic" performed similarly to regular PCL during daily use. When a certain enzyme was applied to the surface of the plastic, however, it eroded the surface of the material and revived the spores encased within. The reanimated bacteria proceeded to start secreting lipase BC again, completely degrading the plastic within six to seven days.
The spores could also be revived by composting the plastic. Samples of the material that were placed in soil thoroughly degraded in 25 to 30 days.
It is important to note that even regular PCL does biodegrade over time, although it takes much longer to do so. In fact, the scientists were able to integrate the spores into non-biodegradable plastics such as polyethylene, then revive the spores back to a lipase-BC-secreting state by grinding up the plastic.
Further research will be required to determine the extent to which these versions of the living plastic are degraded by the enzyme. That said, a team at UC San Diego has already created spore-loaded TPU (thermoplastic polyurethane) which degrades when dumped in a landfill, unlike conventional TPU.
A paper on the study was recently published in the journal Nature Chemical Biology.
Source: Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences
