13:45 〜 14:05
[BBG01-01] Size-dependent biodegradation of chitin in marine environment
★Invited Papers
キーワード：生分解性、キチン、微生物叢
Chitin is the most abundant polysaccharide in the oceans, existing in various living organisms such as crustacean exoskeleton and squid gladius. In nature, chitin molecules assemble into microfibrils, the minimum structural unit. These microfibrils form complexes with proteins and minerals such as calcium carbonate, enabling the exoskeleton to be rigid and tough. Chitin plays an important role in the marine ecosystems as it contains abundant carbon and nitrogen and is highly biodegradable in the marine environment. Therefore, understanding the biodegradation behavior of chitin is important to reveal the key step in oceanic nutrient cycling.
In this study, we investigated the effect of size on the biodegradation behavior of chitin. Chitin was purified from crab shell, and two samples were prepared: flake chitin that underwent only disintegration using a homogenizer (Flake), and nanofibrillated chitin that underwent both disintegration and nanofibrillation using a homogenizer and ultrasonication (Nanofiber). A biochemical oxygen demand (BOD) test was conducted using natural seawater for 14 days to evaluate the biodegradation behavior of the samples.
The Nanofiber samples, treated with both homogenization and ultrasonication, exhibited higher biodegradability (70%) compared with the Flake samples (59%) after the biodegradation test. A remarkable difference was observed in early-stage biodegradation rates: the Nanofiber samples reached 50% degradation in approximately 4 days, whereas the Flake samples took about 11 days. It should be emphasized that both samples were derived from the same raw material and differed only in the nanofibrillation process. Initially, we hypothesized that biodegradation rates would be simply governed by the specific surface area of the samples, with the Nanofiber samples biodegrading faster than the Flake samples due to their increased specific surface area. However, metagenomic analysis revealed completely distinct microbial communities between the Flake and Nanofiber samples after the BOD test, indicating different degradation pathways. This suggests that the samples were biodegraded by different microbiota with varying size preferences, presumably influenced by physical properties such as sample size or accessibility to enzymatic attack, resulting in different biodegradation rates.
In this study, we investigated the effect of size on the biodegradation behavior of chitin. Chitin was purified from crab shell, and two samples were prepared: flake chitin that underwent only disintegration using a homogenizer (Flake), and nanofibrillated chitin that underwent both disintegration and nanofibrillation using a homogenizer and ultrasonication (Nanofiber). A biochemical oxygen demand (BOD) test was conducted using natural seawater for 14 days to evaluate the biodegradation behavior of the samples.
The Nanofiber samples, treated with both homogenization and ultrasonication, exhibited higher biodegradability (70%) compared with the Flake samples (59%) after the biodegradation test. A remarkable difference was observed in early-stage biodegradation rates: the Nanofiber samples reached 50% degradation in approximately 4 days, whereas the Flake samples took about 11 days. It should be emphasized that both samples were derived from the same raw material and differed only in the nanofibrillation process. Initially, we hypothesized that biodegradation rates would be simply governed by the specific surface area of the samples, with the Nanofiber samples biodegrading faster than the Flake samples due to their increased specific surface area. However, metagenomic analysis revealed completely distinct microbial communities between the Flake and Nanofiber samples after the BOD test, indicating different degradation pathways. This suggests that the samples were biodegraded by different microbiota with varying size preferences, presumably influenced by physical properties such as sample size or accessibility to enzymatic attack, resulting in different biodegradation rates.