From Biogeography to Genes: Exploring the Diversity and Evolution of Antarctic Cyanobacteria

The long-term geographic and climatic isolation of Antarctica, combined with strong environmental heterogeneity and extreme conditions, has profoundly shaped the diversity and evolution of its biota. Cyanobacteria are key components of Antarctic microbial ecosystems, yet their biogeographic patterns, including their degree of endemism, remain incompletely understood. This thesis investigated Antarctic cyanobacterial diversity and genomic specificities using complementary ecological and genomic approaches. Analyses of 16S rRNA amplicons from lacustrine and terrestrial habitats showed that both geographic distance and environmental factors structure cyanobacterial communities, with their relative importance varying according to spatial scale and habitat type. Lacustrine communities differed between Antarctica and the sub-Antarctic islands, while terrestrial communities showed strong substrate-specific patterns. Both datasets also revealed substantial proportions of potentially endemic taxa. Comparative genomic analyses of Phormidesmis and Synechococcus-like picocyanobacteria further identified genomic features associated with polar and Antarctic environments, including Antarctic-specific gene clusters and patterns consistent with possible niche shifts and Antarctic ancestry. Together, these results provide a multiscale perspective on cyanobacterial endemism and contribute scientific evidence relevant to the conservation of Antarctic microbial ecosystems.