BE/CBC: Biocomplexity of Marine Stromatolites: Biogeochemical Cycling, Microbial Population Dynamics, and Mineral Formation in a Three Billion Year Old Ecosystem

摘要现代海洋叠层石是一个高度组织化、紧凑的生态系统，特别适合于研究耦合的生物圈-地圈相互作用。美国国家科学基金会最近资助的一项研究结果表明，这些地球上最古老的大型化石的活生生的例子是由三个不同的微生物群落之间的反复过渡形成的，其优势似乎是由微生物种群动态、生物地球化学循环和矿物沉积之间的相互作用驱动的。该生态系统的紧凑性质允许对其组成部分进行采样、实验操作和建模，从而可以评估系统对内部和外部扰动的敏感性，并可以量化生物地球化学循环和矿物形成。因此，它是一个理想的模型系统，用于研究微生物、矿物和环境之间的功能联系，并解决诸如“生物多样性在生物地球化学过程中的作用是什么？地球化学过程对物种丰富度的影响是什么？”微生物如何改变和适应它们的非生物环境？是什么限制了一个看似‘平衡’的状态？是什么力量导致了生态系统的转变？”拟议的研究将使用多种但高度互补的方法，在从单细胞(m)到公里的空间尺度和从分钟到季节和多年的时间尺度上研究叠层石生态系统的复杂性。该计划通过整合自然系统的实地研究、实验研究和定量建模，采用了一种强有力的方法来调查“人口过程和产品”之间的联系。我们对微生物种群的研究将集中在四个主要功能群（蓝藻，好氧异养菌，硫酸盐还原剂和硫化物氧化剂）的组成，丰度和分布上，使用各种技术，包括16S rDNA，末端限制性片段长度多态性分析，荧光原位杂交耦合共聚焦显微镜。实地测量和水槽实验相结合将确定种群、代谢率和化学梯度对水动力条件、沉降和光照变化的反应；化学梯度将使用微电极就地测量。由于外聚合物分泌物（EPS）可能调节质量传输和叠层石内部的交换，因此EPS的结构和组成将使用各种技术进行测量，包括傅里叶变换红外光谱和拉曼光谱，原子力显微镜和GC-MS；溶质通量将用底栖腔测量。EPS性质和元素循环对矿物沉积的影响将通过构建C、O和S预算来确定，辅之以Ca 2+结合研究、显微镜分析以确定活性与微观结构之间的微米尺度关系，以及物种沉淀的培养研究。水槽和实地研究将确定紧急宏观结构的临界侵蚀阈值和侵蚀速率。最后，我们将通过分析稳定同位素、形态计量参数和晶内有机物，寻找保存在岩石记录中的微生物和环境过程的“指纹”。最终，对叠层石系统的全面了解将依赖于定量模型的发展。将开发三种独立的建模方法，它们涉及叠层石生态系统的不同方面：(1)一个成岩模型，它将量化元素循环；(2)建立模拟模型，量化叠层石中元素循环、微生物种群和群落状态之间的相互作用；(3)建立基于阶段的矩阵模型，试图将环境成分与生态系统层面微生物组合的分布和转换联系起来。这些模型将成为理解地球上过去、现在和未来环境中元素循环、微生物种群和沉积之间相互作用的关键工具。促进教育和多学科研究整合的教育活动将包括：(1)本科生、研究生和博士后积极参与实地和实验室研究，以及国际学生交换计划；(2)扩展和维护肋骨公共网站；(3)为公众提供巴哈马叠层石的实地指南。四位欧洲科学家的参与将建立全球网络，继续在新兴的地球微生物学领域进行合作研究。

ABSTRACTModern marine stromatolites are a highly organized, yet compact ecosystem that is uniquely appropriate for studies of coupled biosphere-geosphere interactions. Results from recently funded NSF research indicate that these living examples of Earth's oldest macrofossi s form by repeated transitions among three distinct microbial communities, whose predominance appears to be driven by interactions between microbial population dynamics, biogeochemical cycling, and mineral deposition. The compact nature of this ecosystem allows components to be sampled, experimentally manipulated, and modeled, such that the sensitivity of the system to internal and external perturbations can be evaluated and biogeochemical cycling and minera formation can be quantified. It is thus an ideal model system for investigating functional linkages between microbes, minerals, and the environment and for addressing fundamental questions such as "what is the role of biodiversity in biogeochemical processes and what are the effects of geochemical processes on species richness ?how do microorganisms modify and adapt to their abiotic environment? what constrains a seemingly 'equilibrium 'state and what are the forces that produce ecosystem transitions?" The proposed research will use diverse but highly complementary methodologies to investigate the complexity of the stromatolite ecosystem over spatial scales ranging from single cells (m) to kilometers and temporal scales ranging from minutes to seasonal and multi-annual. The program adopts a powerful approach to the investigation of linkages between 'populations processes and products' through integration of field studies ofnatural systems, experimental studies, and quantitative modeling. Our studies of microbial populations will focus on composition, abundance, and distribution of species in four main functional groups (cyanobacteria, aerobic heterotrophs, sulfate reducers, and sulfide oxidizers) using a variety of techniques including 16S rDNA, Terminal Restriction Fragment Length Polymorphism analysis, and fluorescent in situ hybridization coupled to confocal microscopy. A combination of field measurements and flume experiments will determine the response of populations, metabolic rates, and chemical gradients to variations in hydrodynamic conditions, sedimentation and light; chemical gradients will be measured in situ using microelectrodes. As exopolymeric secretions (EPS) are likely to regulate mass transport and so the exchange within the stromatolites, EPS structure and composition will be measured using a variety of techniques, including Fourier-Transform Infrared and Raman spectroscopies, atomic force microscopy, and GC-MS; solute flux will be measured using benthic chambers. Effects of EPS properties and elemental cycling on mineral deposition will be determined through construction of C, O and S budgets, complemented by studies of Ca 2+ binding, microscopy analyses to define micrometer-scale relationships between activities and microstructure, and culture studies of precipitation by species. Flume and field studies will determine critical erosion thresholds and erosion rates of emergent macrostructures. Finally, we will look for 'fingerprints'of microbial and environmental processes preserved in the rock record through analyses of stable isotopes, morphometric parameters, and intracrystalline organic matter. Ultimately, a full understanding of the stromatolite system will rely on development of quantitative models.Three separate modeling approaches, which relate to different aspects of the stromatolite ecosystem, will be developed -(1)a diagenetic model, which will quantify elemental cycles;(2) a simulation model, which will quantify the interactions between elemental cycles, populations of microbes and community status in the stromatolite and (3) a stage-based matrix model, which will attempt to relate environmental components to the distribution of, and transitions among, the microbial assemblages at the level of the ecosystem. These models will serve as critical tools for understanding the reciprocal interactions between elemental cycles, microbial populations, and sedimentation in past,present, and future environments on earth and beyond.Educational activities that foster the integration of education and multidisciplinary research will include (1) active participation of undergraduates, graduate students, and postdoctoral associates in field and lab studies, and an international student exchange program (2) expansion and maintenance of the RIBS public web site; and (3)a field guide to Bahamian stromatolites for the general public. Participation by four European scientists will establish global networks for continuing collaborative studies in the emerging field of geomicrobiology.