Ocean microbe eaters bite new bio‑plastic【公益科学】

Deep‑Sea Breakthrough: A New Plastic That Disappears in 13 Months

Poly(d‑lactate‑co‑3‑hydroxybutyrate) (LAHB) is a laboratory‑made polyester that can dissolve even in the harsh environment of the deep ocean, where conventional plastics stubbornly persist. Researchers from Shinshu University have proven that deep‑sea microbes can mineralize LAHB in less than a year, leaving only harmless carbon dioxide, water, and a small residue of mineral.

Key Findings

• After 13 months at a depth of 855 m, LAHB lost more than 82 % of its mass.
• Traditional polylactide (PLA) remained entirely intact.
• The plastic’s surface developed cracks and a biofilm of oval and rod‑shaped microbes.
• PLA showed no biofilm or weight loss.

Environmental Context

Worldwide in 2019, the OECD recorded the production of 353 million metric tonnes of plastic. The figure is expected to rise as consumer demand continues to grow. 1.7 million tonnes of plastic waste find their way into the ocean, where gyres trap the debris and create the infamous “garbage patches” in the Pacific, Atlantic, and Indian Oceans.

Why Deep‑Sea Degradation Matters

Deep‑sea conditions—low temperatures, high pressures, and limited nutrients—make plastic breakdown extremely difficult. A polymer that can reliably degrade under these conditions could significantly reduce the amount of plastic that remains trapped in ocean currents.

Research Spotlight

The study was led by Professor Seiichi Taguchi at the Institute for Aqua Regeneration, Shinshu University, with collaborators from the Japan Agency for Marine‑Earth Science and Technology (JAMSTEC) and the Gunma University Center for Food Science and Wellness.

Taguchi explained, “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.”

Methodology

Two variants of LAHB films were submerged along with a conventional PLA film:

• 6% lactate content (P6LAHB)
• 13% lactate content (P13LAHB)
• PLA (control)

They were placed 855 m below Hatsushima Island, where temperature is 3.6 °C, salinity is high and dissolved oxygen minimal.

Results Over 7 and 13 Months

• After 7 months: P13LAHB lost 30.9 % of its weight; P6LAHB showed similar decline.
• After 13 months: P13LAHB lost over 82 %; P6LAHB followed a comparable trend.
• PLA showed no weight loss or visible degradation.

Weighing the Plastisphere

Researchers examined the microbial community—called the plastisphere—that colonized the plastic surfaces. They discovered several specialist groups:

1. Gammaproteobacteria (Colwellia, Pseudoteredinibacter, Agarilytica, UBA7957) produced extracellular poly[3‑hydroxybutyrate] (3HB) depolymerases, which cut long polymer chains into dimers and trimers.
2. Other species (e.g., UBA7959) produced oligomer hydrolases (like PhaZ2), further breaking down dimers into monomers.
3. Alpha‑proteobacteria and Desulfobacterota consumed the monomers (3HB and lactate), converting them into carbon dioxide, water, and residual minerals.

Ultimate Fate of LAHB

Through this cooperative microbial process, LAHB is ultimately mineralized into harmless by‑products that return to the marine ecosystem, while PLA remains intact and contributes to long‑term pollution.

Publication Details

The findings were published in the journal Polymer Degradation and Stability under the title “Unveiling deep‑sea biodegradation of microbially produced lactate‑based polyester (LAHB) via plastisphere metagenomics and metatranscriptomics.”