Abstract:
Antarctic soils represent a unique environment, characterised by extremes of temperature, salinity, elevated UV radiation, low nutrient and low water content. Despite the harshness of this environment, members of 15 bacterial phyla have been identified in soils of the Ross Sea Region. However, the survival mechanisms and ecological roles of Antarctic bacteria are largely unknown. The aim of this thesis is to improve our understanding of the physiological adaptations that give bacterial species their ability to grow and survive in the harsh, nutrient-depleted Antarctic soil environment. For this, three Antarctic strains of the novel bacterial species Paenibacillus darwinianus, isolated in this study, and seven Antarctic members of the bacterial genus Arthrobacter were investigated by whole genome sequencing and phenotypic characterisation. Genome-based comparative analyses with temperate, soil-dwelling counterparts were performed to investigate whether these 10 isolates owe their resilience to substantial genomic changes. Genome analysis of all 10 isolates revealed several genes for signal transduction, sigma factors, the production and/or uptake of compatible solutes, the removal of reactive oxygen species and those for the maintenance of optimal membrane fluidity. However, these genes were also identified in genomes from cold-adapted bacteria and archaea as well as in genomes from temperate, soil-dwelling counterparts. This suggests that these physiological traits are not unique to cold soil environments but are beneficial for growth and survival in a range of soil conditions. Comparative analyses also provided some evidence for genome content scaling in four of the seven Arthrobacter isolates and in all strains of P. darwinianus. In the Antarctic soil environment, complex C sources are largely absent, making a fixed range of labile organic residues the predominant source of C and N. As a result, the maintenance of reproductive efficiency, promoted by smaller genomes, is more crucial for growth and survival than the maintenance of metabolic complexity, promoted by larger genomes. Overall, this study has produced cultured isolates that represent a platform for more in-depth study of novel traits for adaptation to the Antarctic soil environment or for the discovery of novel cold-adapted enzymes for biotechnological uses. In addition, the genome sequences produced are a resource for further investigations into the expression of physiological attributes that enable survival under extreme conditions and the selection processes that affect prokaryotic genome evolution.