Researchers submerged LAHB films at a depth of 855 m near Hatsushima Island to test real-world deep-sea biodegradation. After 13 months, the LAHB plastic lost over 80% of its mass, showing its potential as a safer alternative to conventional plastics that persist in marine ecosystems. Credit: Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Scientists have unveiled a new biodegradable plastic that vanishes in one of the harshest environments on Earth—the deep sea.
In an experiment nearly 3,000 feet underwater, a bioengineered material called LAHB broke down while conventional plastics stayed intact. Deep-sea microbes not only colonized the plastic’s surface, but actively digested it using specialized enzymes, turning it into harmless byproducts. This breakthrough suggests a promising solution to the global plastic crisis, especially in oceans where most waste lingers for decades or centuries.
Global Plastic Waste Problem Still Looms
Plastic pollution remains one of the most urgent environmental challenges, even as bio-based plastics become more common. The OECD’s Global Plastics Outlook (2022) reports that in 2019 the world generated roughly 353 million metric tons of plastic waste, with nearly 1.7 million metric tons ending up directly in aquatic environments. Once there, much of this debris is caught in massive rotating ocean currents called gyres, creating the vast “garbage patches” in the Pacific, Atlantic, and Indian Oceans.
In response, scientists have been working to develop plastics that can reliably degrade even in the extreme conditions of the deep sea. One promising material is poly(d-lactate-co-3-hydroxybutyrate), or LAHB, a lactate-based polyester made with the help of engineered Escherichia coli. Previous studies have shown LAHB can break down in river water and shallow seawater, suggesting its potential as a truly biodegradable option.
First Deep-Sea Test of LAHB Plastic
A new study, released online on July 1, 2025, and appearing in the October 1, 2025, issue of Polymer Degradation and Stability (Volume 240), provides the first evidence that LAHB also biodegrades under deep-ocean conditions. These environments are typically hostile to plastic breakdown due to low temperatures, high pressure, and limited nutrients.
The research was conducted by a Japanese team led by Professor Seiichi Taguchi of the Institute for Aqua Regeneration at Shinshu University, working with Dr. Shun’ichi Ishii from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Professor Ken-ichi Kasuya from the Gunma University Center for Food Science and Wellness.
“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,” explains Prof. Taguchi.
Cold Depths, Strong Results
The research team submerged two types of LAHB films—one containing about 6% lactic acid (P6LAHB) and another with 13% lactic acid (P13LAHB)—alongside a conventional PLA film for comparison. The samples were submerged at a depth of 855 meters near Hatsushima Island, where deep-sea conditions, cold temperatures (3.6 °C), high salinity, and low dissolved oxygen levels make it hard for microbes to degrade plastic.
After 7 and 13 months of immersion, the LAHB films revealed clear signs of biodegradation under deep-sea conditions. The P13LAHB film lost 30.9% of its weight after 7 months and over 82% after 13 months. The P6LAHB film showed similar trends. By contrast, the PLA film showed no measurable weight loss or visible degradation during the same period, underscoring its resistance to microbial degradation. The surfaces of the LAHB films had developed cracks and were covered by biofilms made up of oval- and rod-shaped microbes, indicating that deep-sea microorganisms were colonizing and decomposing the LAHB plastic. The PLA film, however, remained completely free of biofilm.
How Deep-Sea Microbes Break Down Plastic
To understand how the plastic decomposes, the researchers analyzed the plastisphere, the microbial community that formed on the plastic’s surface. They found that different microbial groups played distinct roles. Dominant Gammaproteobacterial genera, including Colwellia, Pseudoteredinibacter, Agarilytica, and UBA7957, produced specialized enzymes known as extracellular poly[3-hydroxybutyrate (3HB)] depolymerases. These enzymes break down long polymer chains into smaller fragments like dimers and trimers. Certain species, such as UBA7959, also produce oligomer hydrolases (like PhaZ2) that further cleave these fragments, splitting 3HB–3HB or 3HB–LA dimers into their monomers.
A Natural Recycling Loop Underwater
Once the polymers are broken down into these simpler building blocks, other microbes, including various Alpha-proteobacteria and Desulfobacterota, continue the process by consuming the monomers like 3HB and lactate. Working together, these microbial communities ultimately convert the plastic into carbon dioxide, water, and other harmless compounds that ideally return to the marine ecosystem.
The findings of this study fill a critical gap in our understanding of how bio-based plastics degrade in remote marine environments. Its proven biodegradability makes it a promising option for creating safer, more biodegradable materials.
A Path Toward a Circular Bioeconomy
“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,” says Prof. Taguchi.
Reference: “Unveiling deep-sea biodegradation of microbially produced lactate-based polyester (LAHB) via plastisphere metagenomics and metatranscriptomics” by Shun’ichi Ishii, Sangho Koh, Miwa Suzuki, Ken-ichi Kasuya and Seiichi Taguchi, 1 July 2025, Polymer Degradation and Stability.
