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Diversity and Metabolism of Endospore-forming Bacteria in Geothermal Sites

Author Sevasti FILIPPIDOU
Director of thesis Prof. Pilar Junier
Co-director of thesis
Summary of thesis



Geothermal activity is observed in sites where geothermal energy is produced and stored, due to seismic and volcanic activity. Undersurface water is heated by this energy and is either directed to the surface drifting along soluble minerals or insoluble substances and results in creating natural hot springs, or it remains underground and is occasionally exploited for human or industrial purposes.

These environments are found to host microbial life. In such habitats, conditions for life in general would be characterized as unfavorable: High temperatures, acidic or alkaline substrates, lack of nutrients, high UV radiation, high concentrations of hazardous components, unfavorable oxygen or hydrogen levels etc. However due to these harsh conditions that exist in such habitats, microorganisms develop survival strategies. Or, these extreme environments favor the existence of microbes that can develop survival strategies. One of these strategies is the procedure of sporulation during which, a vegetative bacterial cell facing these conditions, starts producing a thick-walled spore, which contains its DNA, inside the vegetative cell. In the final steps of sporulation, the vegetative cell is lysed and the spore is freed into the environment. Once conditions become favorable again, the reverse procedure, the germination, takes place and the spore produces a vegetative cell. Endospore-forming bacteria belong to the phylum Firmicutes and are phenotypically very diverse. Aim of this study is to describe the diversity of these bacteria at different geothermal sites around the world, to compare this distribution among sites and to investigate whether there is an association between site and particular assemblage of these bacteria.

Up to present, spores were considered to be in dormant state, meaning that no metabolic activity could be observed. And yet, recent studies have shown that endospore-forming bacteria when in spore state are involved in metal reduction and oxidation procedures. This recent observation yields questions about the interactions of endospore-forming bacteria with their environment, how their metabolisms have evolved under the pressure of these environments and indeed, what these metabolisms are and finally if there is a relation between the diversity and distribution of species with their metabolic capabilities. Aim of this study is to address these questions, as well.

In order to study the microbial distribution by site, the methodological approaches used are enrichment, isolation of bacteria on marine and nutrient agar, microscopic observation, DNA extraction, PCR amplification of 16S rRNA gene and a specific molecular marker for endospore-forming bacteria (the spo0A gene), sequencing and phylogeny. Whole genome sequencing of the isolates, could provide additional information to understand the factors determining the biogeographical distribution of endospore-formers. In order to compare the diversity between cultured and uncultured aerobic endospore-forming bacteria, direct sediment DNA extraction and amplification of 16S rRNA and spo0A genes is performed as well followed by 454 pyrosequencing.

Depending on the results of the diversity study, metabolic experiments will be performed, in various culture media that either promote sediment formation of minerals, or contain different carbon sources. Growth at diverse temperatures and pH conditions will be tested.


Status middle
Administrative delay for the defence