Evolution of cyanobacterial morphotypes

Abstract

Within prokaryotes cyanobacteria represent one of the oldest and morphologically most diverse phyla on Earth. The rise of oxygen levels in the atmosphere 2.32-2.45 billion years ago is assigned to the photosynthetic activity of ancestors from this phylum. Subsequently cyanobacteria were able to adapt to various habitats evolving a comprehensive set of different morphotypes. In a recent study we showed that this evolution is not a gradual transition from simple unicellular to more complex multicellular forms as often assumed. Instead complexity was lost several times and regained at least once. An understanding of the genetic basis of these transitions would be further strengthened by phylogenomic approaches. However, considering that new methods for phylogenomic analyses are emerging, it is unfortunate that genomes available today are comprised of an unbalanced sampling of taxa. We propose avenues to remedy this by identifying taxa that would improve the representation of phylogenetic diversity in this phylum.

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Figures and Tables

Figure 1 Phylogenetic tree of 1,261 cyanobacterial taxa reconstructed by maximum likelihood from 16S rRNA sequences. Morphological sections are marked by color. Fully sequenced strains are indicated on the tree by their taxonomic names. Phylogenetic groups (A1–A5; B1, B2; C1–C4; D1, D2) have been described elsewhere. Four groups for which no genome data are available at present are marked red. Taxa have been selected as previously described in reference 4, with the addition of 41 taxa for which full genome sequences are available.

Figure 2 Phylogenetic tree of a cyanbacterial subset representing the full morphological and genomic diversity. The tree was reconstructed from 16S rRNA sequences using a Bayesian approach. Colors describe different morphological sections. Fully sequenced taxa are shown in black. Shown in red are taxa of groups where no genome sequence data are available at present, and which we recommended for genome sequencing. Taxa have been selected as previously described in reference 4, with the addition of 41 taxa for which full genome sequences are available.

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