Nolwenn Callac (Dr.)

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Phone:+46 (0)708-308755

I am a researcher in geomicrobiology with a background on microbiology, biogeochemistry and isotope geochemistry. My research interest focuses on two main goals: 1) the investigation of the role of the microorganisms in global biogeochemical cycles and how they influence various processes at the interface between hydrosphere, biosphere and geosphere and 2) the investigation and use of biosignatures (isotopic fractionation, mineral alteration) as evidence of (past) life in various settings.

The deep-sea hydrothermal chimneys and sediments host diverse microbial communities with various metabolisms involved in many key biogeochemical reactions in carbon, sulfur, nitrogen and iron cycles; and many studies have demonstrated that microorganisms interact with their environment and could affect vent fluid composition, chimney mineralogy by promoting mineral dissolution or precipitation, and my first research interest is focused on the interactions between the microbial communities and their biotope: mineral substrate and fluid chemistry (hydrothermal fluid, sediment pore water). I am particularly interested in the determination of links between the structure, the activity and the isotopic signatures of microbial communities in function of the physic-chemical characteristics of active hydrothermal systems and reciprocally to determine how the environmental variations could affect the microbial structure, diversity and activity. 

I am also drawn in the functioning of the sulfur and iron biogeochemical cycles in hydrothermal context under different conditions (different temperatures; availability in various carbon, electron donor or acceptor sources; in anaerobiosis or in aerobiosis).

The other aim of my research is to distinguish the biological signatures (isotopic S and Fe biosignatures, bio-mineralization) to the abiotic signatures resulting from abiotic reactions.

To highlight these prokaryotes-biotope relationships, to determine the key microbial player and to determine biosignatures: isotopic and bio-mineralization, I implement a multidisciplinary approach based on microbiology approaches (molecular approaches: PCR, RT-PCR, Q-PCR, ARISA, DGGE, cloning-sequencing, etc…; cultural approaches: batch and in bioreactor mainly in anaerobiosis using various medium), geochemistry analysis (major and trace elements concentration in fluids, mineral description and composition) and isotope techniques (stable isotope: sulfur and iron isotopes).

Then by the examination of the role of microorganisms in environmental condition changes, and by their direct or indirect role in iron and sulfur isotope fractionation and in mineral precipitation could led to a better understanding of the modern deep biosphere and by extension, using the isotopic fingerprint, could allow to access to the microbial activity and metabolisms in the Early Earth and access to potential signatures of (past) life in other planet.