MOCA_Microbial Oceanography of ChemolithoAutotrophic planktonic Communities

Simulation models predict that the oxygen content of the global ocean will decrease by 25% until the end of the century due to an increased stratification of the oceanic surface waters and a rise in temperature. This loss in oxygen will inevitably lead to an expansion of hypoxic and anoxic areas in the global ocean with major consequences for the oceanic carbon and nitrogen cycling. In this proposal, we assess the functional diversity of chemolithoautotrophic prokaryotic communities in two contrasting marine environments, the deep-water masses of the North Atlantic along a latitudinal gradient and around the redoxcline in the central Baltic Sea. Both environments have been shown previously to harbor highly active chemolithoautotrophic prokaryotic communities with dark carbon dioxide fixation rates approaching surface water phytoplankton activity. Specific focus is put on the functional diversity of prokaryotes in the carbon and nitrogen cycling in both systems, including the sulfur cycle in the central Baltic. Biogeochemical rate measurements are tightly linked to functional gene analyses using among other approaches metagenomics and metatranscriptomics. Information obtained from these analyses will guide the development of primers for QPCR to determine the abundance of genes indicative for geochemically relevant processes in the water column of the two systems. Incubation experiments using stable and radio-isotopes in combination with molecular techniques such as SIP-RNA analyses, single-cell analyses using Raman-FISH, NanoSIMS and MICRO-FISH will allow insights into the dynamics of the functional diversity of chemolithotrophic microbial communities in suboxic and anoxic marine planktonic systems. Field studies will be complemented by laboratory model systems with isolated key players in order to understand the adaptive capacity and performance of chemolithoautotrophs in response to different environmental conditions. The combination of these approaches will provide the base for a significant advancement in our understanding of planktonic chemolithoautotrophy in the dark ocean.

Microbial communities in the deep ocean are huge and participate in global carbon cycling. However, the metabolisms of these diverse assemblages of organisms are little understood as most of them cannot be cultivated and studied with traditional microbiological techniques. In the frame of an international collaborative project the capacity of carbon dioxide fixation and carbon consumption by microorganisms in the deep ocean was explored. This subproject focused on the characterization of the genomic potential of Archaea, which are widespread and abundant in the deep ocean, in order to dissect their specific role in the carbon cycle. Both genes for carbon fixation and carbon consumption were found in the genomes of different subgroups of Archaea. Full genomes of a major carbon consuming lineage were reconstructed from samples of the deep ocean and gave detailed insight into the metabolic capacity of the respective organisms. In addition, careful comparative analyses of the genomes of the carbon fixing guild of marine archaea shed light on their metabolic diversity. The huge genomic datasets generated for the deep ocean now serve as a basis for experimental gene expression analyses. These findings and resources represent new ground for the understanding of microorganism and thus for the carbon budget in the deep ocean.