Formation of authigenic minerals associated with microbial activity in ferruginous sediments, Lake Towuti

湖泊环境中的自生矿物可在水柱和沉积物中形成，非生物和/或由生物活动触发。为了使用自生矿物作为湖泊环境的替代物，需要仔细定义它们所指的环境，无论是与特定的沉积输入、水柱过程或沉积物中的微生物活动有关。印度尼西亚的Towuti湖是一个200米深的热带构造盆地，位于超镁铁质岩石中，周围是红壤地区。因此，它的沉积物中含有非常丰富的铁和其他金属，为微生物群落提供了广泛的含金属底物。随着参与生物地球化学循环和早期成岩作用的特定微生物代谢途径的发展，这些元素进一步影响初级生产力。国际地球物理中心计划于2015年5月/6月实施的Towuti钻探项目将包括一个完全用于地球微生物调查的岩芯，该项目将提供机会确定与沉积微生物有关的自生矿物和成岩过程。该项目的主要目标是追踪富含金属的地下沉积环境中的微生物成岩作用，确定微生物在铁矿化中的中介指标，并确定参与铁的生物地球化学循环的微生物的系统发育分布。为此，将结合遗传指纹技术和先进的电子显微镜地球化学分析。首先，我们的分析将检测沉积层位，其中微生物覆盖了先前存在的矿物学。其次，系统发育数据将揭示微生物种类与沉积物矿物学之间的关系，以及生物地球化学循环耦合中的相互作用。第三，它将阐明自生矿物可以明确地用作古代铁建造和地球早期生命的生物特征。总之，本研究项目应对微生物/矿物相互作用以及自生矿物作为湖泊生物地球化学过程的相关指标的使用有新的认识。

Authigenic minerals in lacustrine settings can be formed in the water column and within sediments, abiotically and/or triggered by biological activity. In order to use authigenic minerals as proxies for lacustrine environments, one needs to define carefully the settings to which they refer, whether associated with specific sedimentary inputs, water column processes or microbial activity within the sediment. Lake Towuti, Indonesia, is a tropical 200-m deep tectonic basin seated in ultramafic rocks and surrounded by areas with lateritic soils. As a result, its sediments are very rich in iron and other metals, providing microbial communities with a wide range of metalliferous substrates. These elements further influence primary productivity along with the development of specific microbial metabolic pathways involved in biogeochemical cycling and early diagenesis. The ICDP Towuti Drilling Project scheduled in May/June 2015, which will include a core entirely dedicated to geomicrobiological investigations, will provide the opportunity to identify authigenic minerals and diagenetic processes associated with sedimentary microbes. The main goals of the project are to trace microbial diagenesis within metal-rich subsurface sedimentary environments, define indicators of microbial mediation in iron mineralization and establish the phylogenetic distribution of microorganisms involved in the biogeochemical cycling of iron. For this, a combination of genetic fingerprinting techniques and advanced geochemical analyses by electron microscopy will be applied. Firstly, our analyses will detect sedimentary horizons in which microbes have overprinted the preexisting mineralogy. Secondly, phylogenetic data will reveal the relationship between microbial species and sediment mineralogy as well as mutualistic interactions in the coupling of biogeochemical cycles. Thirdly, it will shed light on authigenic minerals that can be unequivocally used as biosignatures in the context of ancient iron formations and life on the early Earth. Together, the present research project should bring new understanding on microbe/mineral interactions and on the use of authigenic minerals as relevant indicators of biogeochemical processes in lakes.