【Press Release】Crab Shell By-Products Enable Control of the Lifetime of Marine Biodegradable Plastics – A New Method to Delay PHBV Degradation in Seawater by Remodeling the Plastisphere –
A research group from the Graduate School of Food and Population Health Sciences, the Graduate School of Science and Technology, and the Gunma University Center for Food Science and Wellness (GUCFW), Gunma University, in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), has revealed that crab shell by-products generated during seafood processing can be used to regulate the degradation rate of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a marine biodegradable plastic, in seawater.
The study showed that when crab shells were present, the initial attachment of microorganisms to the PHBV surface was suppressed, and the early-stage expression of the gene encoding an enzyme involved in PHBV degradation, exPhaZ, was also reduced. As a result, PHBV degradation was delayed, suggesting that the practical service life of the material could be extended.
The researchers also confirmed a similar effect even when the crab shells were not in direct contact with the PHBV. This finding suggests that the effect was not due simply to physical shielding, but rather to crab shell-derived components that altered the microbial community on the plastic surface, known as the plastisphere.
These findings present a new concept for marine biodegradable plastics: rather than simply increasing their degradability, their lifetime can be tuned according to intended use, while also reusing seafood by-products.
The results of this study were published online in the international journal Polymer Degradation and Stability (Elsevier) on March 24, 2026.
1.Highlights
- Although the marine biodegradable plastic PHBV degrades in seawater, its degradation can be too rapid, creating a challenge for maintaining durability during use.
- When crab shell by-products were present, the amount of microbial attachment on the PHBV surface (biofilm biomass) was reduced to 19–61% of that observed for PHBV alone.
- After 4 weeks, the weight loss of PHBV in contact with crab shells was less than 20% of that of PHBV alone, and even after 8 weeks it remained at 52%.
- Meta-omics analyses showed that the presence of crab shells remodeled the microbial community on the plastic surface and suppressed the early expression of the exPhaZ gene.
- This approach is expected to provide a low-cost and sustainable method for controlling the lifetime of marine biodegradable plastics in the ocean by utilizing seafood by-products.
2.Background
Marine plastic pollution is a global issue, and one promising countermeasure is the use of marine biodegradable plastics, which can be broken down by microorganisms in marine environments.
However, while some materials do not degrade sufficiently in seawater, others degrade too quickly and therefore cannot maintain the durability required during use. Accordingly, marine biodegradable plastics must be designed not only to degrade, but also to retain their performance for the required period and then degrade appropriately afterward.
In this study, the research group focused on PHBV, a type of polyhydroxyalkanoate that is readily biodegradable in marine environments. They hypothesized that crab shells, which are generated in large quantities as seafood processing by-products, might influence the microbial community formed on the PHBV surface in seawater—the plastisphere—and thereby regulate its degradation rate.
Crab shells are a familiar biomass resource composed of chitin, proteins, and minerals, and are known to exhibit high biodegradability in marine environments.
3.Research Findings
In this study, PHBV films were placed in seawater tanks under two conditions: one in which the films were in direct contact with crab shells, and another in which the films were placed in the same tank as crab shells but without direct contact.In both cases, PHBV degradation was clearly suppressed compared with the condition without crab shells.
Measurements of weight loss showed that, when crab shells were present, the weight loss of PHBV during the first 1 to 4 weeks was only 8–20% of that of PHBV alone, and even after 8 weeks it reached only 52%. In addition, the amount of biofilm formed on the PHBV surface decreased to 19–61% of that on PHBV alone.
Scanning electron microscopy revealed that, in PHBV alone, holes and erosion structures appeared on the surface after just 1 week of immersion. In contrast, under crab shell coexistence conditions, no major surface changes were observed up to 4 weeks, confirming that surface deterioration was delayed.Furthermore, because the initial suppression of degradation was observed even without direct contact between crab shells and PHBV, the researchers concluded that the effect was not merely physical shielding, but rather a chemical and biological effect derived from crab shell components.
Analyses of 16S rRNA genes, metagenomes, and metatranscriptomes further showed that the PHBV surface without crab shells was dominated by Oceanospirillum and Bowmanella, whereas under crab shell coexistence conditions, other microbial groups such as Marinobacter became dominant. In addition, the expression of the exPhaZ gene, which is thought to be involved in PHBV degradation, was suppressed at the early stage when crab shells were present.
This is thought to be because chitin and proteins derived from crab shells serve as readily available nutrient sources for microorganisms, reducing their need to preferentially degrade PHBV.
These findings demonstrate a new possibility for materials design: using seafood by-products to engineer the lifetime of marine biodegradable plastics. In the future, this concept may be applied to marine plastic products that are designed to maintain their performance for a required period and then degrade afterward.
4.Publication Information
Journal: Polymer Degradation and Stability
Published online: March 24, 2026
Title: Chitin-Rich Crab Shell By-Products Modulate the Marine Lifetime of PHBV Films via Plastisphere Remodeling
Authors: Phouvilay Soulenthone, Tsukuru Tsukui, Miwa Suzuki, Yuya Tachibana, Shun’ichi Ishii, Hiroyuki Kashima, Yoshiyuki Ishitani, Ken-ichi Kasuya
DOI: 10.1016/j.polymdegradstab.2026.112075
Researchers
Gunma University Graduate School of Food and Population Health Sciences / Gunma University Center for Food Science and Wellness (GUCFW)
Ken-ichi Kasuya, Professor (also affiliated with GUCFW)
Miwa Suzuki, Lecturer (also affiliated with GUCFW)
Phouvilay Soulenthone, Assistant Professor (also affiliated with GUCFW)
Yuya Tachibana, Professor (also affiliated with GUCFW)
Graduate School of Science and Technology
Tsukuru Tsukui, Master’s course graduate student at the time of the research
Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Institute for Extra-cutting-edge Science and Technology Avant-garde Research(X-STAR)
Shun’ichi Ishii, Principal Researcher
Hiroyuki Kashima, Associate Researcher
Yoshiyuki Ishitani, Project Researcher
Funding
This research was supported by the following program:
NEDO (New Energy and Industrial Technology Development Organization), Moonshot Research and Development Program / Realization of Sustainable Resource Circulation toward Environmental Regeneration / Research and Development of Marine Biodegradable Plastics with a Switch Function for the Initiation of Biodegradation (Project Number: JPNP18016; Project Manager: Ken-ichi Kasuya; Project Period: FY2020–FY2027)
Contact Information
For research-related inquiries
Ken-ichi Kasuya, Professor / Director,
Green Polymer Laboratory, Graduate School of Food and Population Health Sciences, Gunma University Gunma University Center for Food Science and Wellness
E-mail: kkasuya@gunma-u.ac.jp
Website: https://sites.google.com/gunma-u.ac.jp/greenpolymergunmalab/home_en
For general inquiries
Sachiko Matsumura
URA Office, Gunma University
E-mail: sacmatsu@gunma-u.ac.jp
For media inquiries
Public Relations Section
Kiryu District Administration Department, Gunma University
E-mail: rikou-pr@ml.gunma-u.ac.jp