Diversity of microorganisms in the Hedera helix phyllosphere and their role in phytoremediation of air pollution

Abstract

Air pollution, containing fossil fuel-related volatile organic compounds (VOCs), constitutes a major problem in most urban areas. According to recent data, more people die from exposure to air pollution than from malaria and HIV infection together. Many years of research show that plant–microbe interactions can be exploited to significantly enhance phytoremediation of contaminated environments. Microorganisms living on plant leaves constitute promising candidates to detoxify harmful VOCs and promote plant growth. Hedera helix, an evergreen plant known for its hardiness and climbing ability, proves to be an excellent host species in the context of phytoremediation of air pollution. We employed 16S rRNA gene amplicon-based metagenomics and real-time PCR to characterize the taxonomic structure of phyllospheric microbial communities associated with H. helix, and compared the communities present at polluted high-traffic locations with non-polluted sites. Further, we investigated bacterial isolates using culture-dependent approaches and sequenced the genomes of promising bacteria with regard to phytoremediation applications. Our results indicate that Actinobacteria, Firmicutes and Betaproteobacteria are more abundantly present on H. helix leaves in a polluted environment. Moreover, the relative composition of the H. helix phyllobiome appears to be similar to that of the model plant Arabidopsis thaliana. We further show that air pollution increases the prevalence of bacterial functional traits affiliated to plant growth and detoxification of fossil fuel-related VOCs. The presence of relevant pathways could be confirmed by genome-level analyses of bacterial isolates showing a high in vitro capacity to metabolize selected VOCs and promote plant growth. In conclusion, an integrated description of the H. helix phyllobiome is presented, including the identification of interesting bacteria with significant potential as inoculants in phytoremediation approaches.