Today's KNOWLEDGE Share:Microbial decomposition of biodegradable plastics on the deep-sea floor:

Today's KNOWLEDGE Share

Microbial decomposition of biodegradable plastics on the deep-sea floor:

Microbes can decompose biodegradable plastics on land, rivers and seashore. However, it is unclear whether deep-sea microbes can degrade biodegradable plastics in the extreme environmental conditions of the seafloor. Here, we report microbial decomposition of representative biodegradable plastics (polyhydroxyalkanoates, biodegradable polyesters, and polysaccharide esters) at diverse deep-sea floor locations ranging in depth from 757 to 5552 m. The degradation of samples was evaluated in terms of weight loss, reduction in material thickness, and surface morphological changes. Poly(L-lactic acid) did not degrade at either shore or deep-sea sites, while other biodegradable polyesters, polyhydroxyalkanoates, and polysaccharide esters were degraded.

Biodegradation at the deep-sea floor:

We investigated the decomposition of representative biodegradable plastics (PHA, biodegradable polyesters, and polysaccharide esters) at the above-described five deep-sea floor locations. Injection-molded samples and films were placed in custom-made sample holders and mesh bags, respectively, and were placed on the deep-sea floor in a condition that prevented physical deformation [samples were placed in polyethylene terephthalate (PET) containers with holes, protected by tennis nets. Installation in the deep-sea and recovery of the samples were performed aboard the Shinkai 6500 human-occupied vehicle (HOV) using a robotic arm. The seafloor soil immediately below the samples was also recovered using a custom-made core and used for microbiological analysis.

Biodegradation of biodegradable polyesters at the deep-sea floor:

The picture shows the overall shapes and morphology of poly[(R)−3-hydroxybutyrate-co-(R)−3-hydroxyhexanoate] (PHBH) injection-molded samples placed on shore (PJM12) and off Hatsushima Island (BHT14) and Minamitorishima Island (AMN13) for approximately 1 year. The PHBH sample shown as an example is one in which degradation had progressed relatively well compared with other samples. The photographs taken from the top and the end after ultrasonic washing and drying, revealed that no physical deformation had occurred. Furthermore, it was confirmed by X-ray diffraction that the crystal structure of samples remained unchanged during the submersion periods at the deep-sea floor and experimental processing. Scanning electron microscopy (SEM) images show the surface profiles after removal of microorganisms from the surface. Whereas the surface morphology before degradation (original) was very smooth, the surfaces of the samples after placement on the shore or the deep-sea floor were observed to be uneven, and degradation was in progress.

source:https://www.nature.com/articles/s41467-023-44368-8