Copy numbers of ribosomal genes show selleck chemical a significant correlation to cyanobacterial species that are capable of terminal differentiation. The formation of heterocysts, morphologically modified cells for nitrogen fixation, requires a strong increase in gene expression, for which an accumulation of ribosomes could be of potential advantage. Further testing would be required though, to make causal conclusions for increased rRNA operons in cyanobacteria belonging to section IV and V. Furthermore, phylogenetic analyses revealed a high conservation of 16S rRNA copies within eubacterial species. Though
this is true for all phyla that have been analyzed, cyanobacteria exhibit an exceptionally strong conservation. Comparison to variation in ITS regions
point to concerted evolution BIBW2992 nmr via homologous recombination and purifying selection as the forces behind 16S rRNA sequence evolution. Comparison of interspecific genetic distances within several prokaryotic phyla, showed significantly lower variation of cyanobacterial 16S rRNA gene sequences. This suggests that 16S rRNA gene sequences evolve by a ‘hypobradytelic’ mode of evolution, previously selleck kinase inhibitor suggested for morphological characteristics in cyanobacteria [56]. Methods Data choice and description For this study we only used cyanobacterial taxa with fully sequenced and annotated genomes publicly available on GenBank
(http://www.ncbi.nlm.nih.gov/genomes/lproks.cgi). Of those 42 genomes (as of August 2011), 36 belong to singlecelled strains, covering 10 different species in total. The remaining six genomes belong to multicellular strains, each representing another species. The taxon sampling was done to exclude a bias towards unicellular closely related cyanobacteria which are overrepresented in the genome-database [57]. Therefore, to cover the widest possible range of morphotypes, we selected one or more, fully sequenced taxa of each species for a total dataset of 22 cyanobacterial strains. More precisely, we included multiple strains of species Cyanothece sp.(2), Resminostat Synechococcus sp.(4), and Prochlorococcus marinus(3), which, following the examination of previous phylogenies [39, 47, 58, 59], are assumed to add phylogenetic diversity. No outgroup was included in the phylogenetic analyses. Gloeobacter violceus has been shown to be closest to eubacterial outgroups [39]. Therefore, phylogenetic trees are represented accordingly. Identification of conserved paralogs and correlation to morphotypes In order to find genes with multiple copies, we applied the orthology prediction algorithm OMA [60] to the set of 22 complete cyanobacteria genomes. First we looked for clusters of highly conserved paralogous genes within each species.