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

Titre : Phenotypic and Genomic Insights Into Ultraviolet Resistance of Arthrobacter and Pseudarthrobacter Isolated From Desert Soil

Auteur : Buckley, Elizabeth

Université de soutenance : Auckland University of Technology

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
Soil microbial communities are important contributors to the desert ecosystem. Top soil is vital for biological activity but is often exposed to large amounts of DNA damaging ultraviolet (UV) radiation. In this thesis, soil bacteria from the Antarctic Dry Valleys and the Namib Desert were investigated for their resistance and sensitivity to UV radiation. The primary objective of this research was to provide genomic insights into how soil bacteria in arid deserts may survive UV radiation. To achieve this objective, abiotic drivers of the bacterial community were investigated, UV resistant bacteria were identified via a rapid screening technique, and whole genome analysis using comparative genomic approaches and predicted protein tertiary structures was carried out. In the first part of this study, the environmental DNA (eDNA) of each desert was investigated to examine the overall bacterial community. This was done using Illumina based 16S rRNA gene-defined community diversity ; for this analysis the V3 and V4 hypervariable regions of the 16S rRNA gene were targeted. Actinobacteria was the most abundant phylum in most of the desert locations. The soil chemistry for the Dry Valleys and the Namib Desert was mostly within the range of published values, except for cation-exchange capacity in the Namib Desert. This range appeared to be influenced by the high concentration of calcium found in the Namib Desert soil. Bacteria isolated from desert soil were exposed to UV radiation using a modified plate drop method for rapid screening of UV resistance or sensitivity. A total of 285 bacterial isolates were tested on solid growth media. All isolates survived exposure to UVA and 35 also survived 10 minutes of 15 W/m2 UVB radiation. In addition, through this method, 16 of the 285 isolates were deemed resistant to 5 W/m2 UVC radiation and 10 were deemed sensitive to 5 W/m2 UVC radiation. Sanger sequencing of the 16S rRNA region using the 27F and 1492R primers identified four genera ; Arthrobacter, Pseudarthrobacter, Pseudomonas and Stenotrophomonas, that contained isolates both resistant and sensitive to 5 W/m2 of UVC radiation. As Actinobacteria was the most abundant phylum identified in the 16S rRNA gene-defined communities, the UV resistance and sensitivity of Arthrobacter and Pseudarthrobacter was further investigated at the genomic level.

Mots clés : Soil ; Bacteria ; Arthrobacter ; Pseudarthrobacter ; Desert ; Namib Desert ; Antarctic Dry Valleys ; Ultraviolet ; UV resistance ; Molecular genomics ; Comparative genomics ; uvrABC

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