Phylogenetic tree of the sequenced cyanobacterial strains and STK information. A phylogenetic tree for 21 sequenced cyanobacteria constructed based on 16s rRNA as was described in Methods. Numbers appearing at the nodes corresponded to the values produced by bootstrap analysis (1000 replicates). Names of marine nitrogen-fixing strains are marked in yellow boxes. Filamentous diazotrophic strains capable of heterocyst differentiation are marked in cyan boxes. This tree is similar to that obtained by Ashby and Houmard . Percentages in brackets represent total STKs as a percentage of total proteins and total additional domains as a percentage of total STKs.