Characterisation and degradation of microplastic by Microbacterium aurantiacum isolated from biofloc in white shrimp aquaculture closed system.

This study pioneers the investigation of a novel bacteria isolated from the biofloc of a recirculating aquaculture system (RAS) for its role as a microplastic degrader. A targeted bioflocculant-producing strain was isolated and identified as Microbacterium aurantiacum (formerly known as Microbacterium chocolatum DSM12507) by phenotypic and genotypic analysis. This strain showed a good flocculation rate (95% in a kaolin test), confirming its capacity as a bioflocculant. To evaluate the performance in the degradation of microplastics (polypropylene (PP), polyethylene (PE) and polystyrene (PS), the Bushnell-Haas (BH) medium with microplastics as carbon source was used. A first screening after 14 days showed clear zones on the agar plates (S1), indicating the release of extracellular enzymes capable of depolymerizing plastic polymers. The results of quantitative gravimetric analysis after 50 days of incubation showed a significant weight loss in all microplastics: 9.2% (PP), 8.9% (PE) and 8.8% (PS), indicating that the microplastic was degraded. This biodegradation was further confirmed by remarkable structural and chemical changes visible on the sample images by spectroscopy analysis. These results suggest that bioflocs from shrimp farming not only represent an unexpected reservoir of bacteria with multiple functions, but can also contribute to environmental control through natural bioremediation. This study has highlighted the identified bioflocculant-producing bacteria, M. aurantiacum as a promising natural agent for the bioremediation of ubiquitous microplastic pollution, transforming a by-product of aquaculture into a potential solution to an environmental crisis.