In vitro study of microbial carbon cycling in subseafloor sediments Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften – Dr. rer. nat. – Am Fachbereich Geowissenschaften Der Universität Bremen vorgelegt von Yu-Shih Lin Bremen Oktober 2009 The PhD thesis was prepared within the Organic Geochemistry Group of the MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Leobener Str., D-28359 Bremen, Germany, between February 2006 and October 2009. 1st Reviewer: Prof. Dr. Kai-Uwe Hinrichs 2nd Reviewer: PD. Dr. Matthias Zabel Additional examiners: Prof. Dr. Wolfgang Bach Dr. Timothy G. Ferdelman Dr. Thomas Pape Date of colloquium: 26 October, 2009 Contents Abstract I Zusammenfassung II Acknowledgements IV 1. Introduction 1Part I. Archaea-dominated marine deep biosphere? 2. Effect of storage conditions on archaeal and bacterial communities in 13subsurface marine sediments 3. Intramolecular stable carbon isotopic analysis of archaeal glycosyl 34tetraether lipids 4. Stable carbon isotope probing of intact polar lipids from benthic 55archaea in marine subsurface sediment Part II. H -fueled carbon cycling 25. Evaluating the extraction-based technique for determination of in situ 77hydrogen concentrations in marine subsurface sediment 6. Microbial formation of methylated sulfides in the anoxic sediment of 101Lake Plußsee, Germany 7.