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

Titre : Characterisation of Pigmentation in a Novel Isolate of Arthrobacter Recovered from Soils of the Namib Desert

Auteur : Vasey, Jack

Université de soutenance : Auckland University of Technology

Grade : Master of Science (Research) (MSc(Res)) 2022

Résumé partiel
The high solar irradiation of desert systems is biologically stressful upon their indigenous soil bacteria, and has major influences on the complexity of their irradiation resistomes (Yuan et al. 2012 ; Paulino-Lima et al. 2013 ; Pavlopoulou et al. 2016 ; León-Sobrino et al. 2019). Characterising features of these bacterial resistomes which confer tolerance to irradiation stress develops our understanding of the breadth of survival systems utilised by extremophiles, and is thus valuable to the field of microbial ecology (Matallana-Surget and Wattiez 2013 ; Pérez et al. 2017).

Arthrobacter sp. NamB2 is a pink-pigmented bacterium from surface soils of the Namib Desert (Buckley 2020). This bacterium demonstrates substantial tolerance to ultraviolet irradiation, and has a corresponding multifaceted intrinsic irradiation resistome (Buckley 2020). The contribution of this bacterium’s pink-pigmentation to its irradiation tolerance was the focus of investigation for this thesis, as pigmentation – particularly the red/yellow pigments of the carotenoid class – have been attributed as a major component in the tolerance of bacteria from other desert systems, including the Atacama and Antarctic deserts (Dieser et al. 2010 ; Silva et al. 2019 ; Flores et al. 2020). Despite the stable, demonstrably microbiologically-harmful solar irradiance of the Namib Desert, no similar investigations of pigmentation as a component of intrinsic bacterial resistomes in this environment have yet been performed. This thesis thus sought to expand knowledge on the breadth of irradiation tolerance systems utilised by extremophiles from regions of high solar irradiance by characterising the role of pigmentation in the irradiation-resistome of Arthrobacter sp. NamB2. To achieve this, the pigment was first identified, while its contributions to irradiation tolerance were investigated via analyses of its light-inducibility in biosynthesis, and pigment-specific mitigation of lethality arising under ultraviolet-A, -B and -C irradiation.

The pigmentation of Arthrobacter sp. NamB2 was extracted and subject to a series of analyses for identification. The extracted pigmentation produced characteristic carotenoid spectral responses under scanning ultraviolet-visible spectroscopy, confirming it was a carotenoid. Chromatographic separation of the pigment extract using thin-layer chromatography and high-performance liquid-chromatography demonstrated the pigment comprised six – eight polarity-discrete carotenoids, each possessing a chromophore thirteen conjugated double bonds in length. Subsequent mass-spectrometry confirmed the presence of the carotenoid bacterioruberin within the extract, and provided evidence for the presence of a number of its commonly co-isolated dehydrated/glycosylated carotenoid variants. The pink-pigment of Arthrobacter sp. NamB2 was thus concluded as carotenogenic in nature, and comprised of a pigment complement specifically based around the carotenoid bacterioruberin.

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