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

湖泊环境中的自生矿物可以在水体和沉积物中形成，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，需要仔细界定它们所指的环境，无论是与特定的沉积物输入、水柱过程还是沉积物内的微生物活动有关。印度尼西亚托乌蒂湖是一个深200米的热带构造盆地，位于超镁铁质岩石中，周围是红土。因此，它的沉积物富含铁和其他金属，为微生物群落提供了广泛的含金属基质。这些元素进一步影响初级生产力，沿着参与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。ICDP Towuti钻井项目计划于2015年5月/6月进行，其中将包括一个完全用于地质微生物调查的岩心，将提供机会识别自生矿物和与沉积微生物相关的成岩过程。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，确定铁矿化中微生物中介作用的指标，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，将采用遗传指纹技术和电子显微镜先进地球化学分析相结合的方法。首先，我们的分析将检测沉积层，其中微生物已经覆盖了先前存在的矿物。其次，系统发育数据将揭示微生物物种与沉积物矿物学之间的关系，以及在地球化学循环耦合中的互利互动。第三，它将阐明自生矿物，这些矿物可以明确地用作早期地球上古代铁形成和生命背景下的生物特征。总之，目前的研究项目应带来新的理解微生物/矿物的相互作用和使用自生矿物在湖泊中的生物地球化学过程的相关指标。

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.