Microplastic-Bacteria Interactions: Toxicity, Colonisation, Degradation and Prospects.

Microplastics (MPs) have established complex bidirectional interactions with bacteria, encompassing both mutualism and antagonism. This review advances a unified 'Stress-Habitat-Degradation' triangular model that systematically integrates three interconnected dimensions: (1) MPs-induced biotoxic stress on bacterial communities in water, soil, guts and plant tissues; (2) the plastisphere as a colonisation substrate that enriches pathogens and facilitates ARG spread; and (3) enzymatic biodegradation by functional taxa like Pseudomonas via specific enzymatic pathways. This framework explicitly links microbial community dynamics to functional outcomes, demonstrating that the same MPs-bacteria interplay simultaneously drives toxicity/pathogen enrichment and beneficial degradation. Environmental factors (temperature, oxygen, soil organic matter) profoundly shape these interactions by regulating gene expression and community succession. Crucially, we identify and resolve apparent contradictions-such as differential Gram-positive/Gram-negative responses and conflicting diversity trends-by attributing them to variations in polymer type, particle size, concentration, exposure time, host species and test conditions. Overall, this synthesis provides a critical integration of MPs-bacterial interactions and proposes a novel pollution control strategy centred on these interactions, redefining environmental risk assessment and bioremediation approaches.