Diversity and evolution of phycobilisomes in marine Synechococcusspp.: a comparative genomics study

Abstract

Phycobilisome diversity and evolution <p>By comparing Synechococcus genomes, candidate genes required for the production of phycobiliproteins, which are part of the lightharvesting antenna complexes called phycobilisomes, were identified. Phylogenetic analyses suggest that the phycobilisome core evolved together with the core genome, whereas rods evolved independently. </p> Abstract Background: Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition. Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II). Among strains containing both phycoerythrins I and II, four subtypes can be distinguished based on the ratio of the two chromophores bound to these phycobiliproteins. Genomes of eleven marine Synechococcus strains recently became available with one to four strains per pigment type or subtype, allowing an unprecedented comparative genomics study of genes involved in phycobilisome metabolism.

Colorful microdiversity of Synechococcus strains (picocyanobacteria) isolated from the Baltic Sea

“…This can be explained in three ways, by extensive homoplasy (backward and/or parallel mutations), horizontal gene transfer of the cpcBA operon or by a lack of data. These results are in line with recent genome analysis of several marine Synechococcus strains, which indicated that genes encoding PC and PE I and II show different evolutionary relationships in comparison with genes of the core genome such as the allo-PC gene or the ribosomal regions (Six et al, 2007). Finally, neighbour-net analysis of the cpcBA phylogeny indicated that the PE-rich isolates of the BSea group are only distantly related to other known Synechococcus isolates ( Figure 5).…”

“…The PE-rich strains could not be differentiated from the PC-rich strains on the basis of their 16S rRNA-ITS sequences. However, this clearly visible phenotypic differentiation was genetically supported by the cpcBA operon, which separated many of the PE-rich strains from the PC-rich strains (Figure 3; see also Six et al, 2007;Haverkamp et al, 2008). Other phenotypic differences, in cell size and cell volume, did not match the separation into different phylogenetic clusters.…”

“…Earlier work has shown that the cpcBA operon of picocyanobacteria can separate strains into different phylogenetic groups with clearly different pigment phenotypes (Six et al, 2007;Haverkamp et al, 2008). Indeed, comparison of the cpcBA operon sequences of our 46 isolates and those available in GenBank shows that the majority of the Baltic Sea isolates clustered according to pigment phenotype (Supplementary Figure SM4).…”

“…Hence, although PE-and PC-rich Synechococcus strains possess similar 16S rRNA-ITS sequences, they have quite different pigmentation (phycobilin) genotypes. Genetic differentiation between PE-and PC-rich strains by the cpcBA operon is ecologically highly relevant, because Synechococcus strains with different pigmentation are adapted to different underwater light climates (Pick, 1991;Vörö s et al, 1998;Wood et al, 1998;Stomp et al, 2004;Six et al, 2007;Stomp et al, 2007a;Haverkamp et al, 2008).…”

“…In the 16S rRNA-ITS phylogeny the Bornholm Sea group is clearly separated from BSea. Other strains that behave in a similar way are CCY0416 (BSea), CCY0490 (Group I), CCY9201 (Bornholm Sea) and the marine Synechococcus strains RS9917 and RCC307 (Figure 3) (Fuller et al, 2003;Six et al, 2007;Haverkamp et al, 2008).…”