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

摘要现代海洋叠层是一个高度有序的紧凑生态系统，非常适合于研究生物圈-地圈耦合作用。来自最近资助的NSF研究的结果表明，这些地球上最古老的大型化石的实例是通过三种不同的微生物群落之间的重复转换形成的，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。这个生态系统的紧凑性允许组件进行采样，实验操作和建模，这样系统的内部和外部扰动的敏感性可以评估和地球化学循环和矿物形成可以量化。因此，它是一个理想的模式系统，用于调查微生物，矿物和环境之间的功能联系，并解决基本问题，如“生物多样性在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来调查叠层石生态系统的复杂性，空间尺度从单细胞（m）到公里，时间尺度从分钟到季节和多年。该计划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，通过整合自然系统的实地研究，实验研究和定量建模。我们对微生物种群的研究将重点关注四个主要功能群（蓝细菌、好氧异养菌、硫酸盐还原剂和硫化物氧化剂）中物种的组成、丰度和分布，使用多种技术，包括16 S rDNA、末端限制性片段长度多态性分析和荧光原位杂交与共聚焦显微镜相结合。结合实地测量和水槽实验，将确定种群、代谢率和化学梯度对水动力条件、沉积和光照变化的反应;将使用微电极就地测量化学梯度。由于胞外聚合物分泌物（EPS）可能会调节物质运输，因此基质层内的交换，EPS结构和组成将使用各种技术进行测量，包括傅立叶变换红外和拉曼光谱，原子力显微镜和GC-MS;溶质通量将使用底栖室进行测量。EPS属性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，并辅之以Ca 2+结合研究、显微镜分析以确定活动与微观结构之间的微米级关系以及按物种对降水的培养研究。水槽和实地研究将确定临界侵蚀阈值和新兴宏观结构的侵蚀率。最后，我们将通过对稳定同位素、形态参数和晶内有机质的分析，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。三个独立的建模方法，涉及叠层石生态系统的不同方面，将被开发：（1）成岩模型，将量化元素循环;（2）模拟模型，它将量化元素循环之间的相互作用，叠层石中的微生物种群和群落状态;（3）基于阶段的基质模型，该模型试图在生态系统水平上将环境组分与微生物群落的分布和过渡联系起来。这些模型将成为理解地球及其他地区过去、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，和一个国际学生交流计划（2）扩大和维护RIBS公共网站;（3）为公众提供巴哈马叠层石实地指南。四位欧洲科学家的参与将建立全球网络，以便在新兴的地球微生物学领域继续进行合作研究。

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.