Researchers in Japan have developed a lactate-based bioplastic that can biodegrade in deep-ocean environments, losing over 80% of its mass after 13 months underwater.
Their research, published in Polymer Degradation and Stability, highlights the potential of poly(D-lactate-co-3-hydroxybutyrate) (LAHB) as an alternative to conventional plastics such as polylactide (PLA), which remain intact under deep sea conditions.
Marine plastic waste continues to accumulate in aquatic ecosystems. The Organisation for Economic Co-operation and Development (OECD) reports that around 353 million metric tons of plastic waste were produced globally in 2019, with nearly 1.7 million metric tons flowing directly into aquatic ecosystems. Some of this debris is trapped in large circulating ocean currents, or gyres, forming persistent floating waste patches.
Investigating degradation on the sea floor
To tackle the issue of plastics in marine environments, research teams around the globe are looking to develop bioplastic alternatives to PLA and other conventional plastics which will breakdown more readily to prevent the build-up of plastic debris.
To test the biodegradability of LAHB in real-world conditions, the researchers submerged plastic samples near Hatsushima Island, Japan, at a depth of 855 meters. The site features low temperatures (3.6 °C), high salinity, limited oxygen and minimal nutrients, all of which slow microbial activity.
The team deployed two types of LAHB films with different lactic acid content – one containing 6% lactic acid (P6LAHB) and another containing 13% (P13LAHB) – alongside a PLA film to act as a control. After 13 months, the P13LAHB sample had degraded by more than 82%, with the P6LAHB showing a similar decline. In contrast, the PLA film exhibited no measurable change in mass or surface characteristics.
“Our study demonstrates for the first time that LAHB, a microbial lactate-based polyester, undergoes active biodegradation and complete mineralization even on the deep-sea floor, where conventional PLA remains completely non-degradable,” commented study author Seiichi Taguchi, a professor at the Institute for Aqua Regeneration, Shinshu University, Japan.
Scanning electron microscopy revealed cracks on the LAHB film surfaces and the presence of microbial biofilms composed of oval- and rod-shaped cells. In contrast, the PLA film remained smooth and biofilm-free.
Enzymes drive stepwise plastic breakdown
To learn more about how the bioplastic breaks down, further analysis focused on the plastisphere – a term given to the microbial ecosystem that forms on plastic surfaces, especially in aquatic environments.
Dominant organisms included genera from the Gammaproteobacteria class, such as Colwellia, Pseudoteredinibacter, Agarilytica, and UBA7957. These microbes secrete extracellular enzymes – specifically poly(3-hydroxybutyrate) depolymerases – that initiate plastic degradation by cleaving long polymer chains into shorter trimers and dimers.
Trimers and dimers
Dimers and trimers are small molecules formed when two or three repeating units (monomers) of a chemical compound join together.
Certain species, such as UBA7959, also produce oligomer hydrolases (like PhaZ2) that further break down dimers and trimers into their monomeric forms.
Additional bacterial groups, including Alphaproteobacteria and Desulfobacterota, continue the breakdown process, metabolizing the resulting monomers. Ultimately, these bacteria convert LAHB into carbon dioxide, water and other environmentally benign compounds.
A potential step toward marine-safe plastics
The study is the first to confirm that LAHB can degrade under high-pressure, low-temperature marine conditions where conventional biodegradable plastics typically fail. The findings provide a data-driven basis for exploring LAHB as a safer material in efforts to reduce marine plastic waste.
“This research addresses one of the most critical limitations of current bioplastics—their lack of biodegradability in marine environments. By showing that LAHB can decompose and mineralize even in deep-sea conditions, the study provides a pathway for safer alternatives to conventional plastics and supports the transition to a circular bioeconomy,” said Taguchi.
Reference: Ishii S, Koh S, Suzuki M, Kasuya K, Taguchi S. Unveiling deep-sea biodegradation of microbially produced lactate-based polyester (LAHB) via plastisphere metagenomics and metatranscriptomics. Polym Degrad Stab. 2025;240:111527. doi: 10.1016/j.polymdegradstab.2025.111527
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