Genome Size of Cyanobacteria

Summary: The genome sizes of 128 strains of cyanobacteria, representative of all major taxonomic groups, lie in the range 1.6 × 109 to 8.6 × 109 daltons. The majority of unicellular cyanobacteria contain genomes of 1.6 × 109 to 2.7 × 109 daltons, comparable in size to those of other bacteria, whereas most pleurocapsalean and filamentous strains possess larger genomes. The genome sizes are discontinuously distributed into four distinct groups which have means of 2.2 × 109, 3.6 × 109, 5.0 × 109 and 7.4 × 109 daltons. The data suggest that genome evolution in cyanobacteria occurred by a series of duplications of a small ancestral genome, and that the complex morphological organization characteristic of many cyanobacteria may have arisen as a result of this process.