Soil microbial responses to nanoplastic particles investigated in transparent soil micromodels

Micro- and nanoplastics have become very common pollutants of soil ecosystems, yet their impact on soil microorganisms remains poorly understood. We exposed a model soil bacterium (Pseudomonas putida) and a model soil fungus (Coprinopsis cinerea) to different concentrations of nanosized polystyrene beads in microfluidic soil chips. The transparent micromodels allowed us to perform direct investigation of the effect of beads on abundance of the microbes and on interactions of individual cells with the nanobeads. Growth of both the bacteria and the fungi was reduced by the exposure to nanoplastics, along with a reduction in bacterial enzymatic activity. Nanobeads were strongly attracted to fungal hyphae, causing a high concentration of beads along the first hyphae to enter a pore space, and thus freeing the surrounding from a large proportion of the beads. We also found plastic particle accumulation along fungal hyphae in setups with soil inocula.  Chips with soil inocula also allowed us to investigate direct interactions of microbes with plastic particles, and particle aggregation under the influence of the microbe-affected soil solution over time. These studies contribute to our understanding of direct toxicity effects and interactions of nanoplastics and soil microbes.