Microbe-Microplastic Axis: Microplastics As Both Microbial Toxin and Tool

Abstract

Microplastics (MPs) in the environment are becoming a growing concern worldwide. Produced by the weathering of plastic waste or through intentional manufacturing, these microscopic synthetic particles are associated with adverse health effects in humans, animals, and even microbes. Due to their small size, MPs have an exceptionally large surface area that, in combination with their intrinsic hydrophobicity and natural weathering, gives them an increased affinity for toxins. Indeed, MPs can contain up to a million times the concentration of heavy metals, organic pollutants, and toxic secondary metabolites compared to their environment. Internalisation of or adherence to MPs by microorganisms has been linked to a decreased growth rate, altered gene expression, lower photosynthetic efficiency, and even cell death. However, despite their toxicity, the microbial utilisation of MPs as tools for protection, carbon and nutrient acquirement, and gene transfer through biofilm formation has now been recognised. Furthermore, microbe-mediated depolymerisation and mineralisation of MPs through the emergence of plastic-degrading enzymes and oxygen radicals highlights the employment of microorganisms as potential solution for the removal of MPs from the biosphere. Yet, it is unlikely that efficient degradation pathways for different types of plastic will evolve naturally in the near future, meaning that alternative approaches must be considered to clean-up the planet. Ultimately, this literature review presents the state of the art on MPs as microbial toxins and tools while exposing the MP-degradation potential of microorganisms and their role in decontaminating the environment.