RESUMEN
Marine Synechococcus cyanobacteria owe their ubiquity in part to the wide pigment diversity of their light-harvesting complexes. In open ocean waters, cells predominantly possess sophisticated antennae with rods composed of phycocyanin and two types of phycoerythrins (PEI and PEII). Some strains are specialized for harvesting either green or blue light, while others can dynamically modify their light absorption spectrum to match the dominant ambient color. This process, called type IV chromatic acclimation (CA4), has been linked to the presence of a small genomic island occurring in two configurations (CA4-A and CA4-B). While the CA4-A process has been partially characterized, the CA4-B process has remained an enigma. Here we characterize the function of two members of the phycobilin lyase E/F clan, MpeW and MpeQ, in Synechococcus sp. strain A15-62 and demonstrate their critical role in CA4-B. While MpeW, encoded in the CA4-B island and up-regulated in green light, attaches the green light-absorbing chromophore phycoerythrobilin to cysteine-83 of the PEII α-subunit in green light, MpeQ binds phycoerythrobilin and isomerizes it into the blue light-absorbing phycourobilin at the same site in blue light, reversing the relationship of MpeZ and MpeY in the CA4-A strain RS9916. Our data thus reveal key molecular differences between the two types of chromatic acclimaters, both highly abundant but occupying distinct complementary ecological niches in the ocean. They also support an evolutionary scenario whereby CA4-B island acquisition allowed former blue light specialists to become chromatic acclimaters, while former green light specialists would have acquired this capacity by gaining a CA4-A island.
Asunto(s)
Proteínas Bacterianas/metabolismo , Complejos de Proteína Captadores de Luz/metabolismo , Liasas/metabolismo , Ficocianina/biosíntesis , Ficoeritrina/biosíntesis , Pigmentos Biológicos/biosíntesis , Synechococcus/metabolismo , Aclimatación , Organismos Acuáticos , Proteínas Bacterianas/genética , Clonación Molecular , Escherichia coli/genética , Escherichia coli/metabolismo , Regulación Bacteriana de la Expresión Génica , Prueba de Complementación Genética , Vectores Genéticos/química , Vectores Genéticos/metabolismo , Islas Genómicas , Luz , Complejos de Proteína Captadores de Luz/genética , Liasas/genética , Ficobilinas/biosíntesis , Ficobilinas/genética , Ficocianina/genética , Ficoeritrina/genética , Filogenia , Pigmentos Biológicos/genética , Subunidades de Proteína/genética , Subunidades de Proteína/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Synechococcus/clasificación , Synechococcus/genética , Synechococcus/efectos de la radiación , Urobilina/análogos & derivados , Urobilina/biosíntesis , Urobilina/genéticaRESUMEN
Recombinant phycobiliprotein can be used as fluorescent label in immunofluorescence assay. In this study, pathway for phycocyanin beta subunit (CpcB) carrying noncognate chromophore phycoerythrobilin (PEB) and phycourobilin (PUB) was constructed in Escherichia coli. Lyase CpcS and CpcT could catalyze attachment of PEB to Cys84-CpcB and Cys155-CpcB, respectively. However, PEB was attached only to Cys84-CpcB when both CpcS and CpcT were present in E. coli. A dual plasmid expression system was used to control the expression of lyases and the attachment order of PEB to CpcB. The production of PEB-Cys155-CpcB was achieved by L-arabinose-induced expression of CpcS, CpcB, Ho1, and PebS, and then the attachment of PEB to Cys84-CpcB was achieved by IPTG-induced expression of CpcS. The doubly chromophorylated CpcB absorbed light maximally at 497.5 nm and 557.0 nm and fluoresced maximally at 507.5 nm and 566.5 nm. An amount of light energy absorbed by PUB-Cys155-CpcB is transferred to PEB-Cys84-CpcB in doubly chromophorylated CpcB, conferring a large stokes shift of 69 nm for this fluorescent protein. There are interactions between chromophores of CpcB which possibly together with the help of lyases lead to isomerization of PEB-Cys155-CpcB to PUB-Cys155-CpcB.
Asunto(s)
Escherichia coli/genética , Escherichia coli/metabolismo , Ficocianina/biosíntesis , Ficocianina/genética , Proteínas Bacterianas/genética , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos/genética , Liasas/genética , Ficobilinas/genética , Ficobiliproteínas/genética , Ficoeritrina/genética , Plásmidos , Urobilina/análogos & derivados , Urobilina/genéticaRESUMEN
Picocyanobacteria of the genus Synechococcus span a range of different colours, from red strains rich in phycoerythrin (PE) to green strains rich in phycocyanin (PC). Here, we show that coexistence of red and green picocyanobacteria in the Baltic Sea is widespread. The diversity and phylogeny of red and green picocyanobacteria was analysed using three different genes: 16S rRNA-ITS, the cpeBA operon of the red PE pigment and the cpcBA operon of the green PC pigment. Sequencing of 209 clones showed that Baltic Sea picocyanobacteria exhibit high levels of microdiversity. The partial nucleotide sequences of the cpcBA and cpeBA operons from the clone libraries of the Baltic Sea revealed two distinct phylogenetic clades: one clade containing mainly sequences from cultured PC-rich picocyanobacteria, while the other contains only sequences from cultivated PE-rich strains. A third clade of phycourobilin (PUB) containing strains of PE-rich Synechococcus spp. did not contain sequences from the Baltic Sea clone libraries. These findings differ from previously published phylogenies based on 16S rRNA gene analysis. Our data suggest that, in terms of their pigmentation, Synechococcus spp. represent three different lineages occupying different ecological niches in the underwater light spectrum. Strains from different lineages can coexist in light environments that overlap with their light absorption spectra.