CuO NP bioactivity in the wheat rhizosphere: Interplay of soil chemistry, root exudation, and biofilms

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This research project explores copper oxide nanoparticle activity at the plant-root interface. Copper oxide is a widely-used nanoparticle (a particle with a diameter below 100 nm) in fungicidal and fertilizer applications; however, plant responses to this material span from toxicity to plant health over a very narrow concentration range. The association of roots with beneficial microbes, both as internal, or endophytic, and external, or epiphytic, colonizers, will influence nanoparticle bioactivity in this zone. A systems approach is employed in this research to identify and elucidate key aspects of nanoparticle-microbe-plant-soil component interactions to better predict the environmental and health implications of this broadly used class of nanoparticles. Detailing the interaction and impact of nanoparticles in the plant root zone colonized with defined bacteria commonly associated with field-grown plants will improve the understanding of the important role of the plant microbiome as well as contribute to guidelines for the safe handling, management, and utilization of engineered nanoparticles. While focusing on a plant system, this research project relates to the essential roles that beneficial microbes play in the health and survival of many organisms, thus the research and associated outreach will augment the growing network of microbiome studies. The main objective of this research project is to identify the combined roles of three major factors, the plant, colonizing microbes, and soil components, that interplay to condition the bioactivity of nanoparticles in the rhizosphere, the zone vital to plant health that exists around a plant root. Two model systems that mimic key elements governing this interplay are being employed. The first system uses a solid growth matrix of silica sand amended with characterized soil pore-waters in order to replicate a key feature of the complex soil solution environment, including inorganic and organic components. Wheat grown in this system will be colonized by microbial isolates from field-grown wheat: A bacillus endophyte isolated from seeds, and a pseudomonad root surface colonizer. These microbes are typical of many isolates that induce plant tolerance to abiotic and biotic stress, such as drought and pathogens. The second system is a root-mimetic, hollow fiber membrane on which microbe colonization, metabolite production, and biofilm formation are being investigated in response to defined ?rhizosolutions? delivered through the fiber lumen. Rhizosolutions constructed from characterized root metabolites permit identification of root metabolites and soil components influencing biofilm formation, bacterial resilience to nanoparticle exposure, and metabolite production in response to the copper oxide nanoparticles, contrasted with responses from bulk copper oxide as well as copper salts. This interdisciplinary project, which merges engineering with chemical and biological sciences, is supporting graduate, undergraduate, and high school students, and underrepresented students from the Utah State University regional campuses through the Native American Summer Mentorship Program (NASMP) in place in the investigators? laboratories. STEM outreach to the general public and K-12 students is involving collaboration with an ARTsySTEM initiative, designed to better link art with science.