SPACIBIO · String-of-pearls: a new bacterial consortium: investigations of lipid biomarkers and their geological significance

Final Activity Report Summary - SPACIBIO (String-of-pearls : a new bacterial consortium: investigations of lipid biomarkers and their geological significance)

Dr Bühring achieved insights into the microbial community and the carbon flow in three different environments with strong geobiological relevance. Her first area of research was located on Kirimati Island, where a multi-method approach for community and functioning analyses of a phototrotrophic microbial mat system of a hypersaline lake was conducted. This approach included microscopic observations, and investigations of the biomarker composition, including intact polar lipids. Experiments with labelled bicarbonate were conducted to pinpoint biomarkers to actively carbon-fixing organisms. A paper has been prepared for submission to Geobiology. The results of this work were additionally presented on the International Meeting of Organic Geochemists 2005 in Seville, Spain, and on the EGU Meeting 2006 in Vienna, Austria. The second area of investigation was located in a mesophilic spring, characterised by high concentrations of reduced sulphur compounds, short-chain gaseous alkanes, and abundant microbial mats that harbour complex prokaryotic communities. Our work at Zodletone spring was part of a collaboration with a microbial observatory project supported by NSF. This environment bears many similarities to environments that existed in the Archean, when oxygen was absent from the Earth's atmosphere and sulphur was largely present in its reduced state and methane was more abundant. Zodletone spring offered the possibility to get insights into a setting that contains abundant anoxygenic phototrophic consortia. In order to link microbial diversity to function, the composition of microbial lipids was investigated and experiments with 13C-labeled substrates were conducted. The experiments revealed an active phototrophic community in Zodletone spring. Dr Bühring is currently preparing the labelling experiments in Zodletone spring for publication. Another publication is planned on the composition of the active microbial community, comparing data from investigation of the intact polar lipids and a RNA-based community analysis. The third area of investigation was the acidic river Río Tinto in southwestern Spain. The Río Tinto is characterised by a very low mean pH value around 2.3 and high concentrations of heavy metals, for example iron, copper, and zinc (Lopez-Archilla AI et al. (2001) Microbial Ecology 41(1): 20-35). The results of this study expose a diverse microbial community at Río Tinto with important contributions from eukaryotes, low abundances of archaea and varying relative amounts of bacteria. Understanding Río Tinto's extremophiles and the molecular signals they leave on the geologic record could provide important clues about how and where life might survive on Mars. As an integral part of this project, a master thesis was completed by Corinna Harms in April 2007. Ms Harms was co-supervised by Dr Bühring; a publication is currently in preparation.

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