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

该项目的实际目标是开发和利用一种称为光谱电化学的新方法，该方法允许在生理溶液条件下使用完整的微生物测量液/固或液/液界面处的电子交换。 虽然该项目将重点关注与矿体内固体矿物交换电子的微生物，但预计同样的实验方法可适用于研究任何液/固或液/不混溶液界面处的任何氧化/还原反应。由此获得的有关此类界面反应机制的基础知识可用于改善人类有目的地利用微生物提取金属以获取商业利益（生物采矿）、将顽固生物质转化为有用的液体燃料（生物燃料生产）、修复大型原油泄漏（生物修复）以及许多其他应用。 直接的人类影响是，2个本科少数民族学生将在该项目的3年每年就业。 由泽维尔大学其他基础设施赠款资助的其他少数民族本科生也有资格参加这个项目。 因此，至少有3或4名少数民族学生将有机会参加这个项目的3 years.Prior研究chemolithotrophic微生物利用一种新的集成腔吸收计（ICAM）进行吸光度测量电子转移反应之间的有色辅基完整的模式生物体，因为他们呼吸好氧可溶性亚铁。 这些研究提出的假设只能通过在好氧和缺氧条件下进行的类似研究来解决。 因此，该项目将产生光谱电化学和动力学测量在完整的细胞在分子氧的存在和不存在。 将测试以下假设：（i）在固体黄铁矿上呼吸的大多数微生物也将直接与固体工作电极交换电子;（ii）分子氧将与阳极电极竞争以回收在阴极波期间引入细菌的电子;（iii）每种微生物将利用相同的末端氧化酶在阴极电子上进行有氧呼吸，就像它在亚铁离子上进行呼吸一样;（iv）氧化的Fe（II）与还原的O2的比率将为4;以及（v）在有氧条件下参与Fe（II）氧化的相同电子转移生物分子也将在厌氧或缺氧条件下参与Fe（III）还原。 将对现有的ICAM进行修改，以在测量过程中排除大气中的氧气，并对现有的观察/反应室进行定制，以优化光谱电化学测量的信噪比。 待检查的完整微生物包括以下属的成员：嗜酸硫杆菌属、纤梭菌属、铁微菌属、硫杆菌属、铁浆菌属和金属球菌属。 这个项目将产生关于这些不寻常的生物体的能量代谢的基本信息。 该项目还将为路易斯安那州泽维尔大学（Xavier University of Louisiana，HBCU）代表性不足的群体的多达12名本科生创造机会，对每个学生都可以称之为自己的项目的一部分进行可持续的研究，在国家科学会议上展示他们的结果，该项目由历史上黑人学院和大学-卓越研究计划（EIR）共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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 minority students will be employed in each of the 3 years of this project. Other minority undergraduate students who are funded from other infrastructure grants at Xavier University will also be eligible to participate in this project. Thus a minimum of 3 or 4 minority students will each have the opportunity to participate in this project for each of the 3 years.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 of under-represented groups at Xavier University of Louisiana, an HBCU, 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.