Intact membrane lipids as tracers for microbial life in the marine deep biosphere Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften - Dr. rer. Nat. – Am Fachbereich Geowissenschaften der Universität Bremen vorgelegt von Julius Sebastian Lipp Bremen Mai 2008 1. Gutachter: Prof. Dr. Kai-Uwe Hinrichs 2. Gutachter: Prof. Dr. Jörn Peckmann Science may set limits to knowledge, but should not set limits to imagination. Bertrand Russel, 1872-1970. TABLE OF CONTENTS Abstract Thesis abstract………………………………………………………….. I Kurzfassung……………………………………………………………. II List of Figures…………………………………………………………………………….. V List of Tables……………………………………………………………………………. VII List of Abbreviations………………………………………………………………….. VIII Chapter I: Introduction……………………………………………………………… 1 General introduction…………………………………………………….. 2 1. The deep biosphere - setting the stage……………………………….. 2. Microbial communities in the deep subsurface……………................. 8 3. Biogeochemical processes - energetic constraints………………….. 14 4. Objectives of this thesis……………………………………………... 16 5. Intact polar lipids as tool in biogeochemistry……………………….. 19 6. Stable carbon isotopes as indicator for metabolic strategies………... 29 7. Contributions to publications……………………………………….. 32 8.