Cell wall components and intact membrane lipids as proxies for investigation of microbial communities in the deep biosphere

In this thesis, three independent methods have been developed and subsequently applied as gene- and cultivation-independent approaches aiming for deciphering microbial community in the marine deep biosphere. These newly developed methods were tailored for analysis of biomarkers with different biochemical functions, i.e. amino sugars, phospholipids (PLs) and low-molecular-weight compounds produced during pyrolysis of microbial biomass. The pyrolysis approach allows rapid detection of microbial signals with minimal sample preparation and sample size. Analysis of amino sugars reveals clues on different microbial sources to organic matter in sediments from the respective study sites, while stable carbon isotopic analysis of amino sugars, in particular for muramic acid and mannosamine, exhibits isotopic imprints of indigenous microorganisms in sediment horizons of enhanced microbial activities. In addition, detection of sedimentary PLs can be significantly improved by the HybridSPE®-based cleanup protocol. Application of this protocol to the Guaymas Basin sediments reveals direct information on the living microbial community at the hydrothermal site. Analysis of these different groups of microbial biomarkers in this thesis extends the toolbox for investigation of microbial processes and provides more comprehensive insights of microbial communities in the deep marine biosphere.