Excellence in Research: Spectroelectrochemical Measurements on Intact Microorganisms Under Oxic and Anoxic Conditions

The practical goal of this project is to develop and exploit a new method, known as spectroelectrochemistry, that permits one to measure the exchange of electrons at liquid/solid or liquid/liquid interfaces using intact microorganisms under physiological solution conditions. Although this project will focus on those microorganisms that exchange electrons with solid minerals within an ore body, it is anticipated that the same experimental method could be adapted to study any oxidation/reduction reaction at any liquid/solid or liquid/immiscible liquid interface.

The fundamental knowledge thus acquired regarding the mechanisms of reactivity at such interfaces could then be used to improve man’s purposeful efforts to exploit microorganisms to extract metals for commercial gain (biomining), convert recalcitrant biomass into useful liquid fuels (biofuel production), remediate large crude oil spills (bioremediation), and many other applications. The immediate human impact is that 2 undergraduate students will be employed in each of the 3-years of this project.

Other undergraduate students who are funded from other infrastructure grants at Xavier University will also be eligible to participate in this project.

Prior studies on chemolithotrophic microorganisms utilized a novel integrating cavity absorption meter (ICAM) to conduct absorbance measurements on electron transfer reactions among colored prosthetic groups within intact model organisms as they respired aerobically on soluble ferrous iron. Those studies generated hypotheses that can be addressed only through similar studies under both oxic and anoxic conditions.

Accordingly, this project will produce spectroelectrochemical and kinetic measurements in intact cells in both the presence and the absence of molecular oxygen. The following hypotheses will be tested: (i) The majority of microorganisms that respire on solid pyrite will also exchange electrons directly with a solid working electrode; (ii) Molecular oxygen will compete with the anodic electrode to recover electrons introduced into the bacterium during the cathodic wave; (iii) Each microorganism will exploit the same terminal oxidase to respire aerobically on cathodic electrons as it does to respire on ferrous ions; (iv) The ratio of Fe(II) oxidized to O2 reduced will be four; and (v) The same electron transfer biomolecules that participate in Fe(II) oxidation under aerobic conditions will also participate in Fe(III) reduction under anaerobic or anoxic conditions.

The existing ICAM will be modified to exclude atmospheric oxygen during measurement, and the existing observation/reaction chamber will be customized to optimize the signal-to-noise characteristics of the spectroelectrochemical measurements. The intact organisms to be examined include members of the following genera: Acidithiobacillus, Leptospirillum, Ferrimicrobium, Sulfobacillus, Ferroplasma, and Metallosphaera.

This project will yield fundamental information on the energy metabolism of these unusual organisms. This project will also create the opportunity for up to 12 undergraduate students to conduct publishable research on a part of the project that each student can call his or her own, to present their results at a national scientific meeting, and to co-author a peer-reviewed paper.

This project is jointly funded by the Historically Black Colleges and Universities - Excellence in Research Program (EiR) and the Directorate of Biological Sciences.

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.