INSPIRE Track 1: Microbial Sulfur Metabolism and its Potential for Transforming the Growth of Epitaxial Solar Cell Absorbers

该奖项的部分资金来自地球科学局海洋科学部的生物海洋学计划和数学和物理科学局材料研究部的电子和光子材料计划。一个简单的想法激发了这个项目：通过表征生活在热液喷口的地下微生物沉积黄铁矿薄膜的机制，能否开发出可控制地生长高纯度黄铁矿薄膜的方法，可以用于生产低成本的光伏太阳能电池？最近对热液喷口进行的现场研究发现，与大型结晶金属硫化物(最大可达1.1毫米)的沉积有关的“地下”微生物，包括黄铁矿。在实验室培养中，通风菌专门沉积了黄铁矿(FeS2)，不含锌、铜和其他液体介质中丰富的金属。非生物孵化没有表现出这种特异性。研究人员假设，微生物在原位通过一系列潜在的过程来沉积黄铁矿，包括一种名为细胞外电子转移(EET)的生理过程，在这个过程中，微生物将电子往返于矿物之间。在现场，EET激活的微生物可能会使用导电矿物以电方式接触氧化剂，并在这些表面沉积黄铁矿。因此，通风口是天然的生物电化学池，通过微生物和非生物电化学过程生长金属硫化物，尽管细节和机制仍有待确定。该项目旨在阐明微生物FeS2黄铁矿生物沉积的机理，并评估如何利用微生物来沉积太阳能电池吸收材料的外延薄膜。FeS_2黄铁矿因其储量丰富、合适的带隙(~0.95 eV)和较高的光吸收系数而被认为是一种有前景的低成本太阳能吸收材料。在较低温度(100摄氏度)下沉积微生物黄铁矿薄膜可能为制造大面积光伏太阳能电池提供一种全新的、低成本的方法。目前对微生物黄铁矿生长的机制知之甚少，尽管大的晶体尺寸表明外延沉积比再成核更受欢迎，这意味着一旦成核，外延生长就可以发生。将利用自然喷口微生物群落和分离进行一系列实验，以确定：A)影响生物沉积的环境因素；B)潜在的分子机制；C)这些薄膜的微观结构和电学性质；以及D)单一物种或联合体的生物沉积是否产生最高纯度、大小和均匀的薄膜。这与我们对微生物硫循环的理解有关，因为人们对微生物如何调节结晶黄铁矿的形成以及这种作用对硫同位素地球化学的影响程度知之甚少。分子研究将被用来询问相关的微生物代谢过程，并限制黄铁矿薄膜生长的可能机制，这对于提高我们生长用于设备应用的FeS_2薄膜的能力至关重要。了解基质结晶学和电导率对生长形态的影响将进一步加深我们对微生物黄铁矿沉积的认识。值得注意的是，这项研究不同于现有的仿生方法。这些研究并不集中于通过拴系肽或合成的细胞外基质进行晶体生长。相反，他们的目标是促进我们对自然生物沉积的理解，利用所获得的见解来种植黄铁矿材料和设备。广泛的影响：除了对创造替代光伏太阳能电池的令人兴奋和可能具有变革性的影响外，这项活动还提供了一个跨越微生物科学和电子/工程材料当前智能边界进行研究的不同寻常的机会。研究生将在PI和博士后的广泛指导下，全面参与这两个领域的工作。通过哈佛大学和国家科学基金会的众多项目，研究人员将让本科生参与这项研究。此外，格吉斯教授和克拉克教授将利用这个项目向一年级学生教授一门新课程，重点是理解和交流跨学科科学。在这门课程中，学生们将与哈佛自然历史博物馆合作，设计一个关于微生物如何制造矿物和电力的公共展览，博物馆工作人员和每年约20万名参观者中的一些人将对其有效性进行评估，从而使哈佛学生能够第一手了解传播科学的知识，并向公众介绍科学与工程之间的关系。

AbstractThis INSPIRE award is partially funded by Biological Oceanography Program in Division of Ocean Sciences, in the Directorate of Geosciences; the Electronic and Photonic Materials Program in the Division of Materials Research, Directorate of Mathematical and Physical Sciences.A simple idea motivates this project: By characterizing the mechanisms underlying pyrite film deposition by subsurface microbes living at hydrothermal vents, can approaches be developed to controllably grow high-purity pyrite films that could be used to produce low-cost photovoltaic solar cells? Recent in situ studies at hydrothermal vents have found "subsurface" microbes associated with the deposition of large crystalline metal sulfides (up to 1.1 millimeters), including iron pyrite. In laboratory incubations, vent microbes specifically deposited pyrite (FeS2), devoid of Zn, Cu and other metals that were abundant in the liquid media. Abiotic incubations did not exhibit this specificity. The investigators hypothesize that, in situ, microbes deposit pyrite via a number of potential processes, including a physiological process called extracellular electron transfer (EET), wherein microbes shuttle electrons to/from minerals. In situ, EET-enabled microbes may use conductive minerals to electrically access oxidants, and deposit pyrite on these surfaces. Vents are thus natural bioelectrochemical cells, which grow metal sulfides via microbial and abiotic electrochemical processes, though the details and mechanisms remain to be determined. This project is aimed at elucidating the mechanisms underlying microbial FeS2 pyrite bio-deposition, and assessing how microbes might be used to deposit epitaxial films for solar cells absorbers. FeS2 pyrite has been identified as prospective low cost solar absorbers because of their abundance, suitable band-gap (~0.95 eV) and high optical absorbance. Microbial pyrite film deposition at lower temperatures (100 C) might offer a radically new, low cost approach to creating large area PV solar cells. Nothing is currently known about the mechanisms underlying microbial pyrite growth, though the large crystal sizes suggest epitaxial deposition is favored over re-nucleation implying that, once nucleated, epitaxial growth can occur. A series of experiments using natural vent microbial communities and isolates will be conducted to determine: A) environmental factors that influence bio-deposition; B) potential molecular mechanisms; C) the microstructural and electrical properties of these films; and D) whether bio-deposition by single species or consortia yields films of highest purity, size and homogeneity.Intellectual Merit: The project is both highly-integrated and transformative. It is relevant to our understanding of microbial sulfur cycling, as little is known about how microbes mediate crystalline pyrite formation and the degree to which this influences sulfur isotope geochemistry. Molecular studies will be used to interrogate relevant microbial metabolic processes and constrain the possible mechanisms of pyrite film growth, which is critical to advancing our ability to grow FeS2 films for device applications. Understanding the effects of substrate crystallography and electrical conductivity on the growth morphology will further inform our knowledge of microbial pyrite deposition. Notably, this research differ from existing biomimetic approaches. The studies are not focused on crystal growth via tethered peptides or synthetic extracellular matrices. Rather, they aim to advance our understanding of natural biodeposition, use the insights gained to grow pyrite materials and devices.Broader Impacts: Apart from the exciting and possibly transformative impact on creating alternative photovoltaic solar cells, this activity offers an unusual opportunity to perform research across current intellectual boundaries of microbial sciences and electronic / engineering materials. Graduate students will be thoroughly engaged in both these areas, with extensive mentoring from the PIs and the postdoc. Via numerous Harvard and NSF programs, the investigators will engage undergraduates in the research. Moreover, Professors Girguis and Clarke will use this project to teach a new course to freshman, focused on understanding and communicating interdisciplinary science. In this course, and in collaboration with the Harvard Museum of Natural History, students would design a public exhibit on how microbes make minerals and electricity, which would be evaluated by the museum staff and the some of the ~200,000 annual visitors on its efficacy, thus enabling the Harvard students to learn firsthand about communicating science, and informing the public about the relationships between science and engineering.