Abstract
Cyanobacteria are major primary producers in the polar and alpine regions contributing significantly to nitrogen and carbon cycles in the cryosphere. Recent advancements in environmental sequencing techniques have revealed great molecular diversity of microorganisms in cold environments. However, there are no comprehensive phylogenetic analyses including the entire known diversity of cyanobacteria from these extreme environments. We present here a global phylogenetic analysis of cyanobacteria including an extensive dataset comprised of available small subunit (SSU) rRNA gene sequences of cyanobacteria from polar and high altitude environments. Furthermore, we used a large-scale multi-gene (135 proteins and 2 ribosomal RNAs) genome constraint including 57 cyanobacterial genomes. Our analyses produced the first phylogeny of cold cyanobacteria exhibiting robust deep branching relationships implementing a phylogenomic approach. We recovered several clades common to Arctic, Antarctic and alpine sites suggesting that the traits necessary for survival in the cold have been acquired by a range of different mechanisms in all major cyanobacteria lineages. Bayesian ancestral state reconstruction revealed that 20 clades each have common ancestors with high probabilities of being capable of surviving in cold environments.
Highlights
Some cyanobacteria can tolerate and even thrive under the extreme conditions found in cold, arid, and UV-exposed environments
Species inference in cyanobacteria is difficult without ecological and physiological data, and many sequences from environmental samples are unclassified, our analyses revealed that several clades contain sequences almost entirely from cold habitats (Figure 2)
It is clear that the cryosphere hosts a high diversity of cyanobacteria our knowledge is by no means complete
Summary
Some cyanobacteria can tolerate and even thrive under the extreme conditions found in cold, arid, and UV-exposed environments. Recent advancements in genome sequencing and improved taxon sampling have helped resolve deep branching relationships of the cyanobacteria tree (Sánchez-Baracaldo et al, 2005; Blank and Sánchez-Baracaldo, 2010; Larsson et al, 2011; Shih et al, 2013; Bombar et al, 2014). While cyanobacterial genomes have helped clarify deep-branching relationships necessary for such analyses, our understanding of the role that cold-tolerant cyanobacteria might have performed in global change has been hindered by an absence of genomes from cold environments. While Jungblut et al (2010) and Martineau et al (2013) employed broader taxon sampling, the extent of the global diversity recovered remains unclear, with poorly resolved relationships between clades
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