Excellence in Research in Spectroelectrochemical Measurements in Intact Microorganisms

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Common means of interrogating chemical reactions that occur between solid surfaces and intact microorganisms typically use light in some manner to monitor either color or fluorescence changes that accompany such reactions. The surfaces of both the solids and the intact microorganisms deflect light and thereby interfere with any optical measurements. This project will provide and validate a new means to conduct light measurements on reactions between solids and live microorganisms. A new instrument with an observation chamber that permits all the light measurements to be harvested and measured will be used, rather than simply losing or ignoring the light that is deflected by the solids or particles in the reaction. This project will focus on 5 to 10 microorganisms that naturally exchange electrons with exterior solid surfaces as part of their lifestyle. It is anticipated that microorganisms with different types of exterior architectures will exchange electrons with exterior solid surfaces using different strategies and colored biomolecules. This project will provide a new means to study biological energy transduction under noninvasive physiological conditions without disrupting the complexity of the live cellular environment. One immediate outcome will be that this project will provide the basic information required to optimize the performance characteristics of microbial fuel cells (novel batteries) at both the anode and the cathode. Undergraduate minority students will be employed in each of 2 laboratories for this project. Overall, a minimum of 8 or more minority students will be trained. The long-term goal of this project is to define the electron transport biomolecules and respiratory pathways in those bacteria that obtain energy for growth from aerobic and anaerobic respiration on soluble and insoluble iron under strongly acidic conditions. Simultaneous spectroelectrochemical measurements and kinetic studies will be conducted to determine the rates of oxygen consumption as selected microorganisms respire in a combination electrolytic/observation cell. To accomplish these goals, this project will implement a new methodology that makes it possible, for the first time, to conduct direct spectrophotometric measurements of in situ electron transfer reactions in living cells under physiological conditions as they accept and donate electrons either directly or indirectly via soluble iron to electrodes immersed in the observation cell. These studies will utilize a novel integrating cavity absorption meter that has an innovative spherical reflecting cavity as its sample observation chamber. Due to multiple reflections at the cavity wall, scattering losses due to sample turbidity are eliminated or minimized because scattered light is prevented from escaping the detector. These combined spectral and oxygen measurements will be conducted while the intact microorganisms are oxidizing and reducing during reversible cyclic voltammetry potentiometric scans. The genera of microorganisms to be studied include, but are not limited to, Acidithiobacillus, Leptospirillum, Acidihalobacter, Sulfobacillus, Ferroplasma, and Metallosphaera, representing 5 of the 6 phyla that contain members that respire on iron. Prior in situ absorbance measurements demonstrated that each of these five microorganisms appeared to express a different set of colored electron transfer biomolecules to respire aerobically on iron. Thus, these studies provide the opportunity to compare and contrast 5 different mechanisms/pathways to accomplish the same metabolic goal of respiring on soluble iron.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.