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

摘要本INSPIRE奖部分资助单位为地球科学局海洋科学部生物海洋学项目；数学与物理科学理事会材料研究部电子与光子材料项目。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膜的机制，是否可以开发出可控制地生长高纯度黄铁矿膜的方法，这些黄铁矿膜可用于生产低成本的光伏太阳能电池？最近在热液喷口的原位研究发现，“地下”微生物与大型结晶金属硫化物（高达1.1毫米）的沉积有关，包括黄铁矿。在实验室培养中，喷口微生物专门沉积了硫铁矿（FeS2），缺乏锌、铜和其他在液体介质中丰富的金属。非生物培养没有表现出这种特异性。研究人员假设，在原地，微生物通过许多潜在的过程沉积黄铁矿，包括一种称为细胞外电子转移（EET）的生理过程，其中微生物将电子传递到矿物质之间。在原位，eet激活的微生物可以利用导电矿物电接近氧化剂，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电池，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。本项目旨在阐明微生物FeS2黄铁矿生物沉积的机制，并评估如何利用微生物沉积太阳能电池吸收剂的外延膜。FeS2黄铁矿因其丰富、合适的带隙（~0.95 eV）和较高的光学吸光度而被认为是一种有前景的低成本太阳能吸收体。低温（100℃）下的微生物黄铁矿膜沉积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方法。目前还不清楚微生物黄铁矿生长的机制，尽管大的晶体尺寸表明外延沉积比再成核更有利，这意味着一旦成核，外延生长就会发生。利用天然喷口微生物群落和分离物进行一系列实验，以确定：A)影响生物沉积的环境因素；B)潜在的分子机制；C)这些薄膜的显微结构和电性能；D)单一物种或群体的生物沉积是否能产生最高纯度、尺寸和均匀性的薄膜。智力优势：该项目是高度集成和变革的。这与我们对微生物硫循环的理解有关，因为我们对微生物如何介导结晶黄铁矿的形成以及这种形成对硫同位素地球化学的影响程度知之甚少。分子研究将用于询问相关的微生物代谢过程，并限制黄铁矿膜生长的可能机制，这对于提高我们培养用于器件应用的FeS2膜的能力至关重要。了解基质晶体学和电导率对生长形态的影响将进一步丰富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。这些研究的重点不是通过栓系肽或合成细胞外基质进行晶体生长。相反，他们的目标是推进我们对自然生物沉积的理解，利用所获得的见解来生长黄铁矿材料和设备。更广泛的影响：除了在创造替代光伏太阳能电池方面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/工程材料当前知识边界进行研究的难得机会。研究生将在pi和博士后的广泛指导下深入研究这两个领域。通过哈佛大学和美国国家科学基金会的众多项目，研究人员将邀请本科生参与这项研究。此外，Girguis教授和Clarke教授将利用这个项目为大一新生开设一门新的课程，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，由博物馆工作人员和每年约20万参观者中的一些人对其有效性进行评估，从而使哈佛学生能够第一手了解科学交流，并告知公众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.