Soil-on-chip for bioremediation studies in PAH-polluted soils: new insights into fungi-bacteria interactions and pollutant dynamics

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) by fungi and bacteria is a sustainable and cost-effective approach for the depollution of soils. However, considering the complexity of soil matrix involving a wide range of parameters, the mechanisms by which microorganisms take up contaminants may vary depending on its composition and endogenous microbial communities. We used a compartmentalized microfluidic device in a soil-on-chip approach to study the bioremediation mechanisms of benzo[a]pyrene (B[a]P) adsorbed on soil-mimicking matrices and real soil particles. These microsystems were observed using confocal microscopy to investigate, at a cellular level, the desorption of B[a]P from soil and its internalization by fungi, either alone or in co-culture with bacteria. Rapidly after the fungal hyphae came in contact with the polluted particles, cellular labelling corresponding to B[a]P was observed, implying that the contaminant was taken up by the fungus. Cellular labelling enabled the localization of pollutant storage sites within model bacteria. Observations about mycelium influence on B[a]P transport and bacterial mobility at microscale were considered alongside macroscopic experiments. Results of this study demonstrate the ability of microorganisms to desorb hydrophobic organic pollutants adsorbed onto soil particles and highlight the potential of microfluidic devices to investigate PAH biodegradation in soils.