Gene-Distribution Patterns on Cyanobacterial Genomes

摘要

In the phylum Cyanobacteria, complete genome sequences have been already reported in seven species and strains. Very interestingly, only one speices of these cyanobacteria, Anabaena sp. PCC7120 (hereafter Anabaena), has considerably large genome sizeof approximately 6.4 Mbr while the remaining species have the genome sizes of 1.7-3.6 Mb to be in the range only from about a quarter to a half of the size of the Anabaena genome. Genome size difference in bacterial species has been well known in the relation between parasitic species such as Mycoplasma and Buchnera and their close relatives. In these cases, genome-size difference has been ascribed to the genome-size reduction, in parasitic species due to their life style of obligate parasitism. On thecontrary, cyanobacterial species whose complete genomes have been sequenced so far are all free-living species. In this study, we approach the genome-size difference in these cyanobacterial species by investigating patterns of gene distribution on the genomes of three cyanobacteria, Anabaena, Synechocystis sp. PCC6803 (ca. 3.6Mb) (hereafter Synechocystis) and Thermosynechococcus elongatus BP-1 (ca. 2.6Mb).