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

Christophe Six,Martin Ostrowski,Laurence Garczarek,David J Scanlan,Frédéric Partensky,Jean-Claude Thomas,Nicolas Blot,Alexis Dufresne

doi:10.1186/gb-2007-8-12-r259

Abstract

By comparing Synechococcus genomes, candidate genes required for the production of phycobiliproteins, which are part of the light-harvesting antenna complexes called phycobilisomes, were identified. Phylogenetic analyses suggest that the phycobilisome core evolved together with the core genome, whereas rods evolved independently.

Highlights

Marine Synechococcus owe their specific vivid color to their large extrinsic antenna complexes called phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition
Synechococcus pigment types Despite the apparently large diversity of pigmentation existing among marine Synechococcus, these can be partitioned into only three major types based on the phycobiliprotein composition of the rods: type 1 representatives have only PC, type 2 have PC and PEI and type 3 have PC, PEI and PEII
The dazzling colors of marine Synechococcus rely on the combination of a few phycobiliprotein forms, which can be assembled into a variety of PBS structures (Figure 7)

Summary

Introduction

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. Synechococcus are often abundant, with cell densities ranging from a few hundred to over one million cells per milliliter of seawater [6,7,8,9,10] Synechococcus cells owe their vivid colors mainly to their photosynthetic antenna, called phycobilisomes (PBSs). These water-soluble macromolecular complexes comprise rods surrounding a central core and are made of phycobiliproteins, which covalently bind chromophores (phycobilins) by thioether bonds to cysteinyl residues (for reviews, see [1115]). In most phycoerythrin (PE)-containing marine Synechococcus characterized so far, PC makes up the basal disc at the core-proximal end of the rods It binds both PCB and the red-colored chromophore phycoerythrobilin (PEB; Amax = 550 nm) at a molar ratio of 1:2 and belongs to the R-PCII type [16]. In strain WH7805, the base of the rods is thought to consist of a so-called R-PCIII, an optically unusual PC that binds PCB and PEB at a molar ratio of 2:1 [15,17]

Methods

Results

Discussion

Conclusion