This NSF award by the Environmental Health and Safety of Nanotechnology program supports work by Professor Shaily Mahendra to examine the effects of copper nanoparticles (NPs) on the diversity and function of bacteria involved in nitrogen cycling in natural and engineered environmental systems.
Background and Significance. We anticipate that in the next few decades, the inputs of engineered nanomaterial-containing products to waste streams will increase, and more plants will be required to carry out tertiary treatment of wastewater. Transformations of nitrogen in the environment are microbially driven; nitrification, denitrification, and nitrogen fixation are catalyzed by specific enzymes, which are sensitive to environmental disturbances and pollution. Additionally, nitrogen management is a significant challenge in agriculture and in wastewater treatment. The rapid growth in production and use of nanomaterials in commercial products has raised concerns about their potential adverse effects on the environment. Our current understanding of the mechanisms of uptake and toxicity towards microorganisms is limited. Furthermore, most toxicological studies evaluate ?manufactured materials? rather than the forms attained after undergoing environmental transformations. We will investigate the regulation of relevant enzymes in pure cultures as well as consortia, thus, addressing issues important to NSF missions of generating a predictive methodology of understanding and mitigating the potential harmful effects of the interaction of NPs with the environment.
Intellectual Merits. This study will test the hypothesis that copper NPs will selectively affect the population, diversity, and activity of bacterial communities involved in nitrogen cycling based on specific nature of NP-cell interactions (ionic copper uptake versus NP uptake; external versus internal dissolution followed by reactive oxygen species (ROS) generation and membrane/DNA/ATP damage; etc.). While there are a few recent reports of short-term toxic effects of NPs on laboratory pure cultures, the novel aspects of this proposal include evaluating NPs? effects on a class of indigenous microorganisms, and the environmental roles they play, over longer time scales. In addition, this will be the first study to explore high-throughput screening (HTS) for evaluating dose-response characteristics as well as mechanisms of NP toxicity. Specific objectives include: (a) to determine the microbial impacts of copper NPs via standard physiological and HTS assays, (b) to investigate the effect of copper NPs on functional gene expression in several pure cultures of nitrifying, denitrifying, anammox, and nitrogen-fixing bacteria in order to identify most susceptible microbial process in the N cycle, and (c) to quantify and model changes in population and diversity of N-cycling bacterial communities, including the effect of intrafloc transport resistance on availability of ionic and particulate copper, nutrients and electron acceptors. pure cultures and microcosms, effect of NPs on the expression of relevant genes will be determined using enzyme-specific assays as well as RT-qPCR. Ultimately, the methodology employed herein will serve as a template to address NP hazard identification and risk assessment, safe design and implementation of nanotechnology, as well as management of global carbon and nitrogen cycles.
Broader Impacts. The broader impacts of the proposed research extend beyond a better understanding of NP interactions with environmentally relevant bacteria. In addition to publications and presentations at scientific meetings, the findings will be translated into a series of lectures to be presented in a new graduate course on Environmental Biotechnology and a redesigned undergraduate course on Environmental Nanotechnology (both taught by the PI). Further, the PI will collaborate with a middle school in Los Angeles Unified School District to develop curriculum for a new environmental science class as well as hands-on activities in the Go Green horticultural club to describe the role of bacteria in environmental cycling of essential elements and assessing the impacts of toxic chemicals. Finally, the PI will serve as the faculty adviser for UCLA chapter of the Society of Women Engineers (SWE), and participate, with the funded Ph.D. students, in meetings and outreach activities.