We then used these hits as edges in a homology graph, and identified clusters of highly conserved paralogs as connected components. Finally, we removed hits within a cluster if the pairwise PF477736 in vivo distance differed significantly from the mean distance within the cluster. In the second step, we grouped detected homologous clusters across species

using OMA alignments, JNJ-26481585 manufacturer but this time with a score cut-off of 180 and minimum sequence identity of ≥50%. We further required that ≥0.8·n i ·n j of hits between any pair of clusters i and j be present in order to be considered, where n i n j is the number of genes in clusters i and j, respectively. If a cluster in one genome grouped with several clusters in another genome, we chose the one with A-1331852 in vitro the lowest average pairwise distance. Again, homologous groups were extracted as connected components from the resulting graph. Finally, single orthologs from the OMA orthologous matrix (i.e, with no detected multiple copies within their originating genome) were matched and added to corresponding homologous groups. We tested whether a correlation between cell differentiation and copy numbers could be observed for the identified genes. To do this,

we devided cyanobacterial species into four different groups of cell differentiation (G0-G3; see results). Five strains belong to G0, 12 taxa belong to G1, Tricodesmium is the only genus in G2, and four species belong to G3. For 16S rRNA genes additional data could be obtained from rrndb-database [45] (Additional file 3). Adding these data resulted in a taxon set of 16S rRNA gene sequences as follows: five strains belonging to G0, 12 strains Bcl-w representing G1, Trichodesmium as the only species in G2 and 11 species in G3. Spearman’s rank and Pearson’s correlation coefficients were applied in order to estimate associations between conserved copy numbers and morphological groups

(G0-G3), using R-software. Correlations with a p-value<0.01 were considered to be significant. Phylogenetic analyses We conducted separate phylogenetic analyses of 16S rRNA gene sequences of cyanobacteria (Table 1) and four different eubacterial phyla (Additional file 10). For all taxa included in the phylogenetic trees, full genome sequences were available. All sequences were downloaded from GenBank [61]. For cyanobacteria two phylogenetic trees were reconstructed. One including a single 16S rRNA sequence per taxon and another including all 16S rRNA copies per taxon. Final taxon sets included 22 sequences in the first case and 48 sequences in the latter. The datasets were aligned using Clustal-X software with default settings [62] (1,325nt incl. gaps). Gaps were excluded from the analysis. Phylogenetic reconstructions were done using Bayesian analysis as implemented in MrBayes software [63].