Understanding microbial manganese-oxidizing communities and physiological mechanisms in metal oxide-rich hydrothermal sediments using a metagenomic and metatranscriptomic approach

热液系统是海洋溶解锰的重要来源。在锰（II）、锰（III、IV）氧化物的氧化作用下，锰（III、IV）氧化物在离源远近的海底以结壳、结核和沉积物的形式沉积。长期以来，人们一直认为微生物活动对这些热液系统中锰的命运至关重要，但我们对催化锰氧化的微生物、锰氧化的机制或锰氧化的生理功能知之甚少。该项目的总体目标是揭示Mn（II）氧化的生物和机制，评估水热Mn氧化剂是否可以从Mn氧化中获得能量，并测试是否存在嗜热性Mn氧化剂。具体而言，该项目将：1)通过比较来自Lau盆地和Loihi海山的锰铁（含锰和铁氧化物）微生物垫与含铁（仅含铁氧化物）微生物垫的元基因组，评估我们是否可以识别出与锰氧化物（以及锰（II）氧化细菌）的存在/浓度相关的某些基因组序列；2)利用与磁性颗粒结合的肽探针选择性结合和捕获氧化锰颗粒，并利用系统发育和功能基因（PCR和FISH）和转录组学分析对颗粒进行表征；3)利用基因组方法、底物刺激（如添加Mn(II)） CO2固定测量和稳定同位素探测（SIP）基因组分析，评估锰铁微生物垫中碳固定的主要途径，并将其与含铁微生物垫相比较，作为Mn基自/混合营养的可能指标；4)分离和表征Mn（II）氧化细菌，确定是否存在嗜热Mn氧化剂。本研究的结果将增加我们对热液沉积物中Mn（II）氧化的理解，确定与环境相关的Mn氧化剂微生物，并开始解决长期存在的问题，即Mn自动/混合营养是否存在，使用的方法不是基于与培养相关的偏差。最终，这些信息对我们理解生物地球化学循环（锰氧化和锰氧化物影响许多其他元素循环，包括碳、硫和重金属）和有毒金属和有机化合物的自然衰减至关重要；这可能导致环境补救技术的改进。由于锰氧化物被认为是光系统II中祖先锰中心的类似物，这项研究也可能为大氧化事件之前发生的古代生物地球化学提供新的见解。更广泛的影响该项目将为一名博士生和一名博士后研究员提供支持和培训，并将通过独立的研究项目和指导为本科生和高素质高中生的教育做出贡献。他们将参加一个针对6-12年级阿拉斯加印第安人教育的地球科学教育项目。此外，该项目还将为一项针对中学教师的培训计划做出贡献，该计划将突出化学、生物和地质在环境中的联系。这项工作的成果将通过简报、出版物和万维网广泛传播。

Hydrothermal systems are important sources of dissolved Mn to the oceans. Upon oxidation of Mn(II), Mn(III,IV) oxides are deposited at the sea floor as crusts, nodules and sediments both near and far from the sources. Microbial activity has long been recognized as being important to the fate of Mn in these hydrothermal systems, yet we know very little about the organisms that catalyze Mn oxidation, the mechanisms by which Mn is oxidized or the physiological function that Mn oxidation serves. The overarching goals of this project are to reveal the organisms and mechanism(s) underlying Mn(II) oxidation, to evaluate whether hydrothermal Mn oxidizers may obtain energy from Mn oxidation, and test whether thermophilic Mn oxidizers exist. Specifically, the project will: 1) evaluate whether we can identify certain genomic sequences that correlate to the presence/concentration of Mn oxides (and hence Mn(II)- oxidizing bacteria) by comparing the metagenomes of ferromanganese (containing both Mn and Fe oxides) microbial mats with ferruginous (Fe oxide only) mats from Lau Basin and Loihi Seamount; 2) use peptide probes bound to magnetic particles for selectively binding and capturing Mn oxide particles and characterizing the particles using phylogenetic and functional gene (PCR and FISH) and transcriptomic analysis; 3) assess the main pathways of carbon fixation in ferromanganese microbial mats as compared to ferruginous mats as a possible indicator of Mn-based auto/mixotrophy using genomic approaches and substrate stimulated (e.g., addition of Mn(II)) CO2 fixation measurements and stable isotope probing (SIP) genomic analysis; and 4) isolate and characterize Mn(II)-oxidizing bacteria and determine whether thermophilic Mn oxidizers exist.Intellectual meritThe results of this research will increase our understanding of Mn(II) oxidation in hydrothermal sediments, identify microorganisms that are the environmentally relevant Mn oxidizers and begin to address the long standing question of whether Mn auto/mixotrophy exists using approaches not based on the biases associated with cultivation. Ultimately this information is critical to our understanding of biogeochemical cycles (Mn oxidation and Mn oxides impact many other elemental cycles, including carbon, sulfur, and heavy metals) and the natural attenuation of toxic metal and organic compounds; this may lead to improved technologies for environmental remediation. Because Mn oxides are believed to be an analog to the ancestral Mn centers in photosystem II, this research may also lend new insights into ancient biogeochemistry occurring before the Great Oxidation Event.Broader impactsThe project will provide support and training for one Ph.D. student and one postdoctoral researcher, and will contribute to the education of undergraduate and highly qualified high school students through independent research projects and mentorships. They will participate in a geoscience education program targeting the education of 6-12 grade Alaskan Native Americans. In addition, this project will contribute to a training program targeted to middle school teachers that highlights the connections between chemistry, biology, and geology in the environment. The results of the work will be broadly disseminated through presentations, publications, and the World Wide Web.