Critical questions remain unanswered regarding the role of the plant holobiont (plants and their microorganisms) on contaminant transformations and plant uptake in the environment. In our research, we investigate the role of the plant endophytes and rhizosphere microorganisms as main drivers for contaminant bioavailability. In one project, we focused on the microbiome role on rare earth elements (REE) plant uptake to promote phytorecovery from waste. In a first study, we investigated the effect of changes on the plant microbiome on the phytorecovery of REE nanoparticles (REE-NP) by exposing ryegrass seeds to REE-NP in hydroponic environments, using microorganisms with REE-dependent metabolism, Methylobacterium extorquens and Bacillus subtilis. Two sets of experiments were performed: bioaugmentation (CeO2 NP and Methylobacterium extorquens AM1), and biostimulation (CeO2 or Nd2O3 NP and endogenous microorganisms). M. extorquens AM1 amendement could not promote NP phytoaccumulation but it enhanced Ce translocation from roots to shoots in sterile seeds. Also, B. subtilis was enriched in control samples, and its relative abundance corresponed with higher Ce extraction in both natural (165 µg/gdried-plant) and surface-sterilized seeds (136 µg/gdried-plant) showing a higher effect of endogenous over exogenous microorganisms’ enrichment. In biostimulation experiments, up to 705 µg/gdried-plant Ce and 19,641 µg/gdried-plant Nd were extracted. SEM-EDS analysis of surface and longitudinal cross section of roots confirmed surface and intracellular accumulation of Nd2O3 nanoparticles. We have used tested bioaugmentation on REE-enriched waste pile samples (~ 8,000 ppm Total REE) from Eastern Adirondack Highlands, New York. Mine waste bioaugmentation and biostimulation were investigated by adding an enrichment solution of 70% M. extorquens AM1, and methylamine hydrochloride with and without mineral medium to support microbial growth. The greatest REE cellular accumulation was obtained in the bioaugmented experiment with only methylamine hydrochloride (without mineral medium), with 557 µg/gcell total REE, the higher concentration of Ce (215 µg/gcell). Hence, the addition of M. extorquens and an exogenous carbon source and electron donor promotes REE biouptake. The outcome of this research aims to a better understanding of bio-interaction between bacteria and rare earth elements and leads to designing new systems to remediate wastes while extracting valuable materials.

Harnessing the plant holobiont for pollution control and resource recovery

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ACS Spring 2023

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