Presentation Information
[P02-248]Effects of molecular structure on aerobic biodegradation behavior and microbial responses of cellulose esters in marine environments
○Hiroyuki Itaya1,2, Ao Oshikiri1, Hiroto Morita1, Wilasinee Kotcharoen2, Yutaka Takeuchi2, Naoki Wada2, Kenji Takahashi2 (1. Graduate School of Natural Science and Technology, Kanazawa University (Japan), 2. Faculty of Biological Science and Technology, Kanazawa University (Japan))
Keywords:
Marine biodegradation,Biobased polymers,Biodegradable polymers,Biochemical oxygen demand (BOD),Surface-associated microbial communities
The accumulation of persistent plastics in marine environments has increased the demand for biodegradable, bio-based polymeric materials. Cellulose esters are a promising alternative to petroleum-derived plastics because their properties can be tuned by controlling their molecular structure, particularly the type and degree of substitution (DS). However, systematic evaluations of aerobic biodegradation behavior in marine environments remain limited, and the microbial responses associated with cellulose ester degradation are still poorly understood. In this study, we investigated the effects of molecular structure on the aerobic biodegradation of cellulose esters in seawater, focusing on the commercially important cellulose acetate (CA) and cellulose propionate (CP).
CA and CP samples with varying DS values were systematically synthesized. Aerobic biodegradability was evaluated using biochemical oxygen demand (BOD) measurements based on ISO 23977-2:2020, enabling the quantitative determination of mineralization rates. Microbial colonization on the polymer film surface was further investigated using a seawater-supplied flow-through aquaculture system. Films of CA and CP were immersed, and the biofilms formed on their surfaces were analyzed by 16S rRNA gene sequencing to identify structure-dependent differences in bacterial community composition.
For CA, high mineralization comparable to microcrystalline cellulose was maintained up to a DS of 2.0, followed by a sharp decrease at a DS of 2.4. Conversely, CP exhibited such high mineralization only at a DS of 0.4, with a pronounced decline at a DS of 1.0 and a negligible mineralization rate at a DS of 2.1 and above. These results demonstrate a clear threshold for the degree of substitution dependence in aerobic biodegradation, showing that even slight changes in DS significantly affect enzyme activity and microbial mineralization efficiency. CP shows particularly high sensitivity to increases in DS. Microbial community analysis further revealed that CA and CP films developed distinct bacterial communities despite exposure to identical seawater conditions.
The observed differences in microbial community composition indicate that polymer chemical structure influences not only biodegradation rates but also the selection and succession of surface-associated microbial communities. The lower DS threshold observed for CP suggests that the chemical nature of the acyl substituent enhances the sensitivity of biodegradation to molecular substitution under aerobic marine conditions.
This study demonstrates that the aerobic biodegradation of cellulose esters in marine environments is governed by molecular structure, particularly the degree of substitution. The identification of clear DS-dependent thresholds, together with structure-dependent microbial responses, provides insights into the rational design of cellulose-based polymers compatible with natural microbial degradation processes in marine environments.
CA and CP samples with varying DS values were systematically synthesized. Aerobic biodegradability was evaluated using biochemical oxygen demand (BOD) measurements based on ISO 23977-2:2020, enabling the quantitative determination of mineralization rates. Microbial colonization on the polymer film surface was further investigated using a seawater-supplied flow-through aquaculture system. Films of CA and CP were immersed, and the biofilms formed on their surfaces were analyzed by 16S rRNA gene sequencing to identify structure-dependent differences in bacterial community composition.
For CA, high mineralization comparable to microcrystalline cellulose was maintained up to a DS of 2.0, followed by a sharp decrease at a DS of 2.4. Conversely, CP exhibited such high mineralization only at a DS of 0.4, with a pronounced decline at a DS of 1.0 and a negligible mineralization rate at a DS of 2.1 and above. These results demonstrate a clear threshold for the degree of substitution dependence in aerobic biodegradation, showing that even slight changes in DS significantly affect enzyme activity and microbial mineralization efficiency. CP shows particularly high sensitivity to increases in DS. Microbial community analysis further revealed that CA and CP films developed distinct bacterial communities despite exposure to identical seawater conditions.
The observed differences in microbial community composition indicate that polymer chemical structure influences not only biodegradation rates but also the selection and succession of surface-associated microbial communities. The lower DS threshold observed for CP suggests that the chemical nature of the acyl substituent enhances the sensitivity of biodegradation to molecular substitution under aerobic marine conditions.
This study demonstrates that the aerobic biodegradation of cellulose esters in marine environments is governed by molecular structure, particularly the degree of substitution. The identification of clear DS-dependent thresholds, together with structure-dependent microbial responses, provides insights into the rational design of cellulose-based polymers compatible with natural microbial degradation processes in marine environments.
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