BioMetArchive - Subsurface biosphere metagenomics along the 1 Ma sedimentary archive of ferruginous Lake Towuti, Indonesia.

• Applicant: Dr. Aurèle Vuillemin
• Subject Area: Microbial Ecology and Applied Microbiology ; Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497135959

Lake Towuti, Sulawesi, Indonesia is a stratified ferruginous system whose deep basin experienced dynamic redox conditions with variable iron oxide inflows over geologic time. In summer 2015, the ICDP Towuti Drilling Project retrieved a stratigraphic archive spanning the last 1 Ma of climatic and depositional history. During the Late Quaternary, wet and dry periods alternated, resulting in variable trophic and redox conditions. As sediment accumulated, microbial life at the sediment surface, linked to the availability of metal and organic substrates, became entombed, archiving paleoenvironmental conditions. However, changing environmental conditions during burial will select for specific groups of microorganisms, thereby altering the primary genomic record. Recent ICDP studies reported contrasting results with regard to the suitability of genomic data for reconstructions of paleoenvironmental conditions. The BioMetArchive project will investigate how sedimentological and geochemical conditions select for specific microbial assemblages at the time of deposition and trace them through the 1 Ma chronosequence. We will further elaborate on Lake Towuti as a modern analog for microbial processes in ancient ferruginous systems. The two main hypotheses of the project are: (1) Microbial compositions initially arise from past lacustrine conditions and deposited substrates, and are partially recorded in sedimentary DNA; (2) environmental conditions at depth select for specific metabolic features which allow the subsurface biosphere to persist in Lake Towuti and which are similar to processes that operated in ancient ferruginous systems.Thanks to recent advances in metagenomics, sedimentary DNA can now be used to characterize microbial populations in terms of abundance, diversity and metabolic functions. The BioMetArchive project will utilize sediments sampled at high resolution during field operations in 2015 and since kept deeply frozen at -80°C. Recent tests proved the suitability of this material for our planned analyses. We will establish the phylogenetic distribution of microorganisms and integrate genomic data with already existing environmental and geochemical datasets to identify parameters that control microbial community composition over time. Through metagenomics we will identify which microbial taxa and metabolic features are involved in iron reduction and organic matter remineralization throughout the sediment sequence. Finally, we will reconstruct metabolic pathways that can drive efficient redox cycling and organic matter remineralization in ferruginous sediments. The sediment’s ferruginous conditions predominantly select for fermentative Bathyarchaeota. Metabolic features assigned to this entirely uncultivated phylum relate to iron and sulfur transformation and methanogenesis, suggesting cryptic biogeochemical cycling. The deep biosphere of ferruginous Lake Towuti thereby represents a modern counterpart of early life’s metabolic processes.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1006: International Continental Scientific Drilling Program (ICDP)
• Co-Investigator: Dr. Jens Kallmeyer