Influence of alteration of mafic and ultramafic rocks on the diversity and adaptation of associated microbial communities

• Main Author: Lecoeuvre, Aurélien
• Other Authors: Université Paris Cité, Bénédicte Ménez, Emmanuelle Gérard
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2020
• Subjects: Deep biosphere; Oceanic crust; Serpentinization; Basalt alteration; Abiotic carbon compounds; Metagenomics; Biosphère profonde; Croûte océanique; Serpentinisation; Altération des basaltes; Carbone organique abiotique; Métagénomiques; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Indian; Iceland
• Online Access: https://theses.hal.science/tel-03259020; https://theses.hal.science/tel-03259020/document; https://theses.hal.science/tel-03259020/file/LECOEUVRE_Aurelien_vd2.pdf

The subsurface is considered as the largest habitat on Earth hosting the majority of microbial biomass and species diversity. The oceanic crust constitutes the largest aquifer of our planet where water-rocks reactions provide sources of aiotic carbon and energy from which deep microbial communities may flourish in the absence of light. In the framework of this thesis, we focused on two major subsurface hydrothermal processes, namely the aqueous alteration of crystalline basalts and the serpentinisation of peridotites, with the aim to study the influence of rock alteration on the associated microbial communities’ ecology. To this aim, microbial communities diversity and their metabolic potential were characterized for (i) the recently discovered serpentinite-hosted hydrothermal field, namely the Old City hydrothermal field (OCHF), located on the eastern region of the ultraslow southwest Indian ridge (SWIR) and (ii) a basaltic aquifer influenced by anthropogenic gas injections at Hellisheiði, Iceland. Metagenomic approaches revealed that microbial diversity and metabolisms at OCHF depend on the relative influences of serpentinization-derived fluids and seawater. Moreover, our results suggested strong heterogeneities within and between hydrothermal vents, likely due to diffuse hydrothermal fluid venting. In these vents, the microbial niches are potentially partitioned at the microscale according to the relative contribution of serpentinization derived hydrothermal fluids and seawater, hence providing different pools of nutrients. A major outcome of this thesis is that putatively serpentinization influenced microbial phylotypes at OCHF are closely related to microorganisms from ophiolitic serpentinite-hosted ecosystems rather than to its unique oceanic analog, namely the Lost City hydrothermal field (LCHF). Considering that the OCHF is located in the most amagmatic region of the SWIR whereas gabbros are widespread below the LCHF, we postulated that magmatic intrusions impacting both the protolith mineralogy and ...