Microbial Plastic Degradation Works Better as a Multispecies Division of Labor

Biodegradable plastics are increasingly being viewed as a potential solution to plastic pollution in the environment, as they are expected to shorten the residence time of these materials in natural systems and ultimately allow microorganisms to convert them into carbon dioxide and biomass.

（感謝 Foster MJ et al. (2026) 提供）

Among the many biodegradable plastics currently in use, aromatic aliphatic copolyesters combine two distinct chemical features within the same material. The aromatic portion provides structural strength and durability, making these polymers functionally comparable to conventional polyethylene terephthalate (PET), whereas the aliphatic portion improves enzymatic accessibility, allowing enzymes to more easily access, bind, cleave, and degrade the material. Although this design appears to balance performance with environmental degradability, it also introduces an important complication: once a polymer contains multiple chemically distinct subunits, its degradation can no longer be completed by a single microorganism.

Polybutylene sebacate-co-terephthalate (PBSeT), the polymer examined in this study, is composed of terephthalic acid (TPA), sebacic acid (SA), and 1,4-butanediol (Bd). These three monomeric components enter entirely different metabolic pathways. TPA is an aromatic dicarboxylic acid that must first be processed by ring-dioxygenase enzymes and converted into protocatechuic acid before it can be funneled into central carbon metabolism. SA is an aliphatic dicarboxylic acid that is primarily metabolized through β-oxidation-like pathways. Bd, by contrast, must first undergo oxidation of its terminal alcohol groups into carboxylic acids before it can be further utilized. At present, no single bacterial species is known to carry out all of these transformations on its own.

Molecular structures of P3HB and PBSeT（圖片來源：Foster MJ et al. (2026)，CC0 1.0 公共領域）

To investigate how this chemically complex polymer is degraded, the researchers enriched a 30-member bacterial community from the Mediterranean Sea and examined how these organisms functioned together. This consortium included representatives from Alphaproteobacteria, Gammaproteobacteria, Bacilli, and Flavobacteriia. By constructing this defined microbial community, the study was able to directly test how different bacterial species cooperate during polymer degradation.

When this bacterial consortium was incubated with the simpler polyester poly(3-hydroxybutyrate) (P3HB), more than half of the polymer-derived carbon was mineralized to carbon dioxide within only 11 days. In contrast, PBSeT was mineralized far more slowly, with only about 4.6% converted to carbon dioxide after 41 days. This difference indicates that PBSeT degradation is slower and constrained by multiple sequential transformation steps.

The most important finding of the study lies in the level of functional specialization. When the bacterial strains were tested individually, no single bacterium was able to fully consume all components of PBSeT. Some bacteria exhibited strong esterase activity and could depolymerize the polymer into smaller molecules, yet could not further metabolize all of the products released. Other bacteria lacked the ability to initiate polymer breakdown but were capable of consuming specific intermediate products. When these organisms were present together, they formed a continuous metabolic chain that enabled a degradation process that none of them could complete alone.

One particularly important species in this system was Pseudomonas pachastrellae. This bacterium played a key role in the first step by depolymerizing the bulk polymer into soluble smaller molecules. However, Pseudomonas pachastrellae could not consume all of the resulting products by itself. It therefore depended on complementary bacteria, such as Pseudooceanicola nitratireducens or Peribacillus frigoritolerans, to carry out downstream metabolic steps. Together, these bacteria formed a complementary metabolic partnership that enhanced overall mineralization.

During PBSeT degradation by this bacterial consortium, multiple intermediate products were generated, including compounds associated with TPA, SA, and Bd. These intermediates were often highly transient because once they were produced, they were rapidly consumed by other bacteria in the community. This "produce-and-immediately-consume" dynamic makes it extremely difficult to track degradation pathways in natural environments and helps explain why earlier studies often relied only on indirect inference rather than direct experimental evidence.

This pattern closely resembles the degradation of other chemically complex organic materials in nature. Whether the substrate is lignin, cellulose, or petroleum-derived hydrocarbons, degradation generally depends on the coordinated activity of multiple microorganisms, each contributing different enzymes and metabolic capabilities. Plastics, especially durable high-molecular-weight polymers, are therefore even less likely to be fully degraded by a single organism acting alone.

If future biodegradable plastics are to be genuinely effective in real environmental settings, it will not be sufficient to consider only the chemical structure of the material itself. Their fate will also depend on the functional composition of the surrounding microbial community. Likewise, strategies for bioremediation or plastic pollution mitigation should not focus only on identifying the "best" single bacterial strain. A more realistic and effective approach will be to understand how to build, support, or stimulate multispecies microbial communities with complementary metabolic functions. Only through this kind of cooperative system can higher-efficiency plastic degradation be achieved under natural environmental conditions.

Author: Shui-Ye You

Reference:

Foster MJ et al. (2026). Complementary Bacterial Functions Enhance Mineralization of Aromatic Aliphatic Copolyesters within a Marine Microbial Consortium. Environmental Science & Technology.