Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Adaptation of two microbial communities to low water potential

Anpassung von zwei mikrobiellen Gemeinschaften an niedriges Wasserpotenzial

Auteur : Gracia Alvira, Juan Bosco

Université de soutenance : Universität Wien

Grade : Masterarbeit 2022

Résumé
Desiccation and hyper-salinity are often treated as the same stress since both lead to the reduction of bioavailable water in the environment. Microorganisms adapted to these stresses have developed survival strategies like sporulation, metabolic dormancy, biosynthesis and accumulation of compatible solutes, expression of catalases, ROS scavengers and organisation in multi-species stratified biofilms. However, it is still not clear which of these adaptations are specific to either desiccation or hyper-salinity and which are common to both stresses. Our primary goal was to gain insights into the adaptation strategies of microorganisms adapted to arid and hyper-saline environments. We investigated two microbial communities that endure low water bioavailability : a desert biological soil crust and a hyper-saline microbial mat. We used FISH to evaluate the changes in the ribosomes content in cells from the desert biological soil crusts upon hydration. We saw increase in the FISH detection rate and the signal intensity throughout the 12 h incubation period, suggesting increase in the protein synthesis potential upon hydration. We looked at the spatial distribution of Archaea, Bacteria and Alphaproteobacteria throughout the depth profile of two hyper-saline microbial mats with different salinity levels using CARD-FISH. We compared the relative abundance of the taxa of study with metagenomic reads estimations from the same samples. Relative abundance diverged between CARD-FISH and metagenomic reads estimations, but both methods detected a decrease in the Alphaproteobacteria relative abundance in the middle layer of the mat under low salinity. Finally, we searched for potential habitat-specific adaptation strategies in closely related genomes sequenced from arid and saline environments. Although phylogeny was more important than adaptation to the environment in terms of genomic content, we found several strategies shared by closely related bacteria from both habitats, like ion transport, and strategies that were characteristic from hyper-saline bacteria, like compatible solutes transport. From our work we can conclude that desiccation and hyper-salinity are different stresses and have different impact on the genome, despite leading both to lower water activity.

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