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Ben-Gurion University of the Negev (2020)

Desert soil bacterial dynamics during a seasonal hydration event

Šťovíček, Adam

Titre : Desert soil bacterial dynamics during a seasonal hydration event

Auteur : Šťovíček, Adam

Etablissement de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2020

Deserts comprise the largest terrestrial biome, stretching over 30% of the Earth’s surface. Yet, desert soil is largely an unknown ecosystem that could serve as a unique model to study interactions and dynamics of soil microbial communities, devoid of plant interferences. Several studies have explored desert soil microbial dynamics associated with soil wetting during seasonal rain events. However, these studies largely ignored the inevitable desiccation that further change soil commu nities. Here, we present the results of an extensive study conducted in the Negev Desert in Israel during seasonal rain events, following the soil microbial dynam ics with Illumina based amplicon sequencing of the bacterial ribosomal RNA. The obtained results were combined with mathematical modelling soil populations’ re sponse to hydration-desiccation cycles and with a mesocosmos study testing the effects of hydration intensity and temperature modes under controlled conditions. Our results portrayed a dramatic shift of the soil bacterial communities following a rain event and a gradual return to the original composition during desiccation. Upon hydration we observed a significant decrease in diversity, which we link to an increase in connectivity that enhanced competition, as demonstrated by the in silico model. To validate our results, we studied the potential bias introduced by the reverse transcription reaction conditions on the sequenced bacterial community. To this end, we compared three commonly used reverse transcriptases under two temperature modes, applied on ribosomes extracted from the same soil samples and compared the resulting communities. Our results indicated up to a six- fold differ ence between bacterial classes among the different conditions, some of which can be explained by the GC content and temperature effects. However, a large portion of the observed differences could not be explained by these measures. Our results suggest that the use of ribosomes to describe changes in soil bacterial communities should consider potential biases and follow pre-defined reaction settings. We further conclude that the ribosomes sequencing together with mathematical modeling pro vide novel insights into the mechanisms and dynamics of arid soil microbial diversity during hydration-desiccation cycles.

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Page publiée le 7 janvier 2022