Aeonium decorum as a microbial recruitment platform for atmospheric polycyclic aromatic hydrocarbons mitigation in urban gardens

BACKGROUND: In the context of the Sustainable Architecture, green roofs, green walls, green belts or urban farms are becoming popular infrastructures in cities and have been proposed as promising elements to ameliorate air pollution. Atmospheric contaminants are deposited not only on the foliar surface of plants, but also in soils. Plants may interact with pollutants, but their associated microbiomes (epiphytic, endophytic and rhizospheric) may harbor contaminant-degrading bacteria which could play an important role in pollutant mitigation. Therefore, we explored the effects of atmospheric contaminants, using naphthalene as a model compound, on some of the living elements of urban gardens (plants and microbiomes). RESULTS: Exposure to gaseous naphthalene had weak effects on Aeonium decorum and Trifolium repens plants (measured as efficiency of photosystem II), and on soil bacterial diversity. Although the presence of naphthalene is not the major driver of soil bacterial community structure, metagenomic and qPCR analysis revealed an increase in polycyclic aromatic hydrocarbon (PAH)-ring hydroxylating dioxygenases in Aeonium planted soils, suggesting a positive effect of this plant species for the selection of potential contaminant-degrading microbes. We have also observed an increment in Pseudomonas (known for their capacity to degrade contaminants) and Solimonas in response to naphthalene. Validation of tools designed to evaluate the exposure of plants to atmospheric contaminants was performed creating urban gardens planted with A. decorum plants and exposed to environmental conditions. CONCLUSIONS: Our results suggest that Pseudomonas and Solimonas could be used as markers for biodegradation. A. decorum is proposed as a good candidate for amelioration of atmospheric contaminants and gardens constructed with these plants carried PAH degrading bacteria on leaf surfaces indicating that they have the capacity to respond to the presence of contaminants.