FIG. 3.

Distance tree of the cyanobacteria constructed on the basis of almost complete 16S rRNA gene sequences (more than 1,400 nucleotides, in black). Evolutionary distances were determined by the Jukes-Cantor equation, and the tree was calculated with the neighbor-joining algorithm. The 16S rRNA gene sequence from Escherichia was used as an outgroup sequence. Partial sequences (ca. 325 nucleotides [red] and ca. 610 nucleotides [blue]) were integrated into the tree by applying a parsimony criterion without disrupting the overall tree topology established beforehand. Sequence designations for environmental sequences (in orange) correspond to those in Table 1. The tree has been simplified by collapsing coherent clusters of strains into boxes of fixed height. In each box, the shortest and longest sides depict the minimal and maximal distance to the common node of all sequences contained within the cluster. Each of the six clusters of interest in this study is shown in detail on the left. Clusters in red are composed exclusive of desert crust cyanobacterial sequences. All entries are named after database labels, without taxonomic considerations.