Protists can move readily through unsaturated soils and chemotact towards bacterial prey, which are abundant at growing tips of plant roots. Many protists species are indiscriminate eaters, capturing and ingesting bacteria-sized objects in the soil. Protists may therefore serve as transport vehicles for polymer-coated agrochemicals and introduced plant growth promoting rhizobacteria (PGPR): accumulating prey-sized particles, transporting the “payload” through soil, and targeting delivery to the growing root tips. We developed a transport assay comprised of an emulated soil micromodel to screen candidate soil protists for performance in taking up, transporting, and depositing fluorescent microspheres or polymer-encapsulated nanoparticles through the emulated physical structure of sandy loam soil. Next, we created a mesoscale transport assay containing real sandy loam soil and a live Medicago truncatula plant within a 3D-printed device, referred to here as “µ-rhizoslides”. Using the µ-rhizoslides, we studied the most promising protist candidate from the transport assay. We tracked position of fluorescent particles or fluorescent protein-expressing PGPR (bacteria) on a weekly basis in replicate µ-rhizoslides that either contained or did not contain live protists (Colpoda). We demonstrate inclusion of Colpoda facilitated transport of fluorescent particles and of bacteria along growing plant roots. µ-rhizoslides containing protists exhibited bacterial cells located further down plant roots compared with bacteria-only µ-rhizoslides. Even though protists are natural predators of the bacteria used in transport assays, the inclusion of protists still enhanced transport of bacteria to the distal region of plant roots: the portion most in need of colonization by PGPR. Facilitating transport and targeting delivery of valuable agrochemicals or bacteria to the tips of growing plant roots will greatly facilitate the implementation of more sustainable no-till farming practices, reduce overall agrochemical use, improve surface water quality, and may dramatically reduce or even reverse the net impact of the agriculture sector on global climate change.

Microbial-mediated transport of beneficial bacteria and agrochemicals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.