Dissecting the black box of microbially mediated pyrite formation from FeS and H2S

剖析微生物介导的 FeS 和 H2S 黄铁矿形成的黑匣子

• 批准号: 435849387
• 负责人: Professor Dr. Michael Pester
• 金额: --
• 依托单位: Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/435849387?language=en
• 关键词: Dissecting; black; box; microbially; mediated

The exergonic reaction of FeS with H2S to form FeS2 (pyrite) and H2 was postulated to have operated as an early form of energy metabolism on primordial Earth. Since the Archean, sedimentary pyrite formation played a major role in the global iron and sulfur cycles, with direct impact on the redox state of the atmosphere. However, the mechanism of sedimentary pyrite formation and the way microorganisms contribute to this process is still being debated. This year, we published work on the first enrichment culture, which is capable to grow with FeS, H2S, and CO2 as sole substrates to produce FeS2 and CH4 (Thiel et al., 2019, PNAS). This proposal aims to elucidate the mechanism behind microbially mediated pyrite formation coupled to methanogenesis. Two hypotheses will be tested to unravel whether pyrite formation in enrichment J5 is directly involved in energy conservation or not. Hypothesis I (H-I) will address the question whether microorganisms involved in pyrite formation could potentially utilize the Wächtershäuser reaction, i.e. the direct formation of FeS2 and H2 from FeS and H2S for energy conservation. This would necessitate long-distance electron transport from the cell surface into the cytoplasmic membrane or cytoplasm, e.g. involving multiheme cytochrome c complexes. Hypothesis II (H-II) will test whether the energy metabolism of the non-methanogenic partner is restricted to a reversal of sulfur respiration (sulfide conversion to zero-valent sulfur and H2), with subsequent pyrite formation being mediated by the (possibly abiotic) reaction of the formed zero-valent sulfur with FeS. The two hypotheses will be tested in three complementary work packages (WP). In WP1, high quality draft genomes of enrichment J5 members will be obtained by metagenomics and annotated in respect to their potential energy metabolism including hallmark proteins indicative of H-I or H-II. Subsequent metatranscriptomics will follow expression of genes encoding such hallmark proteins. In WP2, individual community members in enrichment J5 will be identified by fluorescent in situ hybridization in combination with single-cell RAMAN microspectroscopy. The latter will serve the identification of RAMAN signals indicative of overexpressed multiheme cytochrome c redox complexes (H-I) or the formation of zero-valent sulfur within or associated with microbial cells (H-II). In WP3, enrichment J5 will be exposed to alternative growth conditions, which are postulated to require similar enzyme complexes as laid out in H-I and H-II. This will include the oxidation of elemental Fe under sulfate-reducing conditions (H-I) and the oxidation of hydrogen with elemental sulfur to H2S (H-II). Upon positive growth, expressed genes will be followed by metatranscriptomics. The proposed project will be important to establish enrichment J5 as a model for microbial pyrite formation, which has impact for our understanding of biogeochemical sulfur and iron cycling and origin-of-life-hypotheses.

FeS与H2S形成FeS 2（黄铁矿）和H2的放能反应被认为是原始地球上能量代谢的早期形式。太古代以来，沉积黄铁矿的形成在全球铁硫循环中起着重要作用，直接影响着大气的氧化还原状态。然而，沉积黄铁矿形成的机制和微生物对这一过程的贡献方式仍存在争议。今年，我们发表了关于第一富集培养物的工作，其能够以FeS、H2S和CO2作为唯一底物生长以产生FeS 2和CH 4（Thiel et al.，2019年，PNAS）。这一提议旨在阐明微生物介导的黄铁矿形成与甲烷生成的机制。两个假设将进行测试，以解开富集J5中的黄铁矿形成是否直接参与节能与否。假设I（H-I）将解决参与黄铁矿形成的微生物是否可能利用Wächtershäuser反应的问题，即从FeS和H2S直接形成FeS 2和H2以节省能量。这将需要从细胞表面到细胞质膜或细胞质中的长距离电子传递，例如涉及多血红素细胞色素c复合物。假设II（H-II）将测试非产甲烷伙伴的能量代谢是否仅限于硫呼吸的逆转（硫化物转化为零价硫和H2），随后的黄铁矿形成由所形成的零价硫与FeS的（可能是非生物的）反应介导。这两个假设将在三个互补的工作包（WP）中进行测试。在WP 1中，富集J5成员的高质量草案基因组将通过宏基因组学获得，并就其潜在的能量代谢进行注释，包括指示H-I或H-II的标志蛋白。随后的元转录组学将跟踪编码这些标志蛋白的基因的表达。在WP 2中，将通过荧光原位杂交结合单细胞拉曼显微光谱来鉴定富集J5中的个体群落成员。后者将用于鉴定指示过表达的多血红素细胞色素c氧化还原复合物（H-I）或在微生物细胞内或与微生物细胞相关的零价硫（H-II）的形成的拉曼信号。在WP 3中，富集J5将暴露于替代生长条件，假定其需要与H-I和H-II中所述相似的酶复合物。这将包括元素Fe在硫酸盐还原条件下的氧化（H-I）和氢与元素硫氧化成H2S（H-II）。在阳性生长时，表达的基因将随后进行元转录组学。建议的项目将是重要的，以建立富集J5作为微生物黄铁矿形成的模型，这对我们的地球化学硫和铁循环和生命起源假说的理解有影响。