Healthy and resilient soil ecosystems are essential to help mitigate and adapt to climate change, but pressure on soil systems is increasing. Enhancing natural attenuation processes is a sustainable alternative for the restoration of soils contaminated by organic chemicals represented by PAHs and co-occurring compounds. The flow of hydrophobic contaminants to degradative microbial communities in soil can be significantly affected by microbial positioning along the contaminant paths, which may result in enhanced or diminished biodegradation rates. In this study, the flagellated bacterium Pseudomonas putida G7, which degrades pyrene by cometabolism, was cultivated and prepared differently for soil slurry experiments, metabolite analyses and greenhouse experiments. Additionally, we integrated passive dosing with 14C-labeled pyrene, inoculation of motile bacteria into soil and a complete sunflower (Helianthus annuus L.) ontogenic cycle to evaluate a new scenario related to pollutant transformation and risk in soil. A preliminary evaluation of possible risks to human and ecosystems were also done. Our results showed that the plants facilitated bacterial access to the distant pollutant source, possibly by increasing bacterial dispersal in the soil; this increased bacterial access was associated with cometabolism. Cometabolism of this PAH occurred immediately in the inoculated and shaken soil slurries, where the bacteria had full access to the passive dosing devices (silicone O-rings). Furthermore, the resulting metabolites were not only mobilized into the soils leachates but also taken up by the plants, accumulating in the roots at significantly higher proportions in inoculated samples than in uninoculated controls and acting differently on their way to the fruits. This new, proof-ofconcept scenario successfully showed that bacterial cometabolism may contribute to the environmental risk from PAHs in soil by improving pollutant mobilization and uptake by plants. These results are relevant in the bioremediation field because they show how inoculated bacteria can be mobilized by plants to reach distant pollutant sources and how partial pollutant transformation may generate further issues. Our results may also contribute to other pollution management sectors, such as wastewater treatment and prospective risk evaluation of agrochemicals, where rhizosphere microorganisms play a relevant role

Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.

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