Characterizing the toxicity of engineered nanoparticles to nitrogen-fixing soil bacteria

Nanoparticles are increasingly found in many novel engineering applications, due to their size, 1-100nm. This property gives them more reactive surface area per volume and creates unique interaction pathways from the bulk forms of a substance. This has led to improvements in pharmaceutical, cosmetic, electronic, and agricultural technologies to name a few. However, the interactions of engineered nanoparticles (ENPs or NPs in this proposal) with biological systems is largely not yet understood, and should be investigated in order to anticipate potentially negative side-effects of ENPs as they inevitably enter the environment.

Rhizobia are a class of bacteria possessing the ability to symbiose with legume plants, forming nodules on their roots which are capable of fixing and supplying nitrogen in exchange for the host's carbon. This feature makes rhizobia key players in global nitrogen cycling, and crucial to the overall health and productivity of the agroecosystem. By helping supply a significant amount of nitrogen demands worldwide, the demand for synthetic fertilizer drops. This lowers the extensive use of fossil fuels in the production of these fertilizers, farmers' expenses, and helps mitigate the risk of excess fertilizer leaching into the environment and harming local aquatic ecosystems by eutrophication. Therefore, this interaction is important to protect in the interest of sustainable agricultural practices, and the toxicity of ENPs to it should be characterized in order to safeguard these resources in the event of ENP release into the environment.

There are numerous studies demonstrating the toxicity of ENPs to plants, animals, and bacteria, but few involving rhizobia or rare earth element ENPs. Therefore, the aim of my experiments will be to begin characterizing the toxicity of Neodymium (Nd) and Ytterbium (Yb) oxide nanoparticles from the Lanthanide series of the periodic table, as well as add to current knowledge base on the toxicity of copper oxide and silver nanoparticles, in regards specifically to Bradyrhizobium bacteria. I will do so using both in vitro and in vivo scenarios, and methods including growth and viability tests, and ICP-MS.