Chlorophylls (Chls) are essential cofactors for photosynthesis. One of the least understood steps of Chl biosynthesis is formation of the fifth (E) ring, where the red substrate, magnesium protoporphyrin IX monomethyl ester, is converted to the green product, 3,8-divinyl protochlorophyllide a In oxygenic phototrophs, this reaction is catalyzed by an oxygen-dependent cyclase, consisting of a catalytic subunit (AcsF/CycI) and an auxiliary protein, Ycf54. Deletion of Ycf54 impairs cyclase activity and results in severe Chl deficiency, but its exact role is not clear. Here, we used a Δycf54 mutant of the model cyanobacterium Synechocystis sp. PCC 6803 to generate suppressor mutations that restore normal levels of Chl. Sequencing Δycf54 revertants identified a single D219G amino acid substitution in CycI and frameshifts in slr1916, which encodes a putative esterase. Introduction of these mutations to the original Δycf54 mutant validated the suppressor effect, especially in combination. However, comprehensive analysis of the Δycf54 suppressor strains revealed that the D219G-substituted CycI is only partially active and its accumulation is misregulated, suggesting that Ycf54 controls both the level and activity of CycI. We also show that Slr1916 has Chl dephytylase activity in vitro and its inactivation up-regulates the entire Chl biosynthetic pathway, resulting in improved cyclase activity. Finally, large-scale bioinformatic analysis indicates that our laboratory evolution of Ycf54-independent CycI mimics natural evolution of AcsF in low-light-adapted ecotypes of the oceanic cyanobacteria Prochlorococcus, which lack Ycf54, providing insight into the evolutionary history of the cyclase enzyme.

• Klíčová slova
• chlorophyll, cyanobacteria, cyclase, microevolution, photosynthesis,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• bakteriochlorofyly biosyntéza   genetika   MeSH
• delece genu * MeSH
• oxygenasy genetika   metabolismus   MeSH
• Prochlorococcus genetika   metabolismus   MeSH
• Synechocystis genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• oxygenasy MeSH

Aerobic anoxygenic phototrophs (AAPs) are prokaryotic microorganisms capable of harvesting light using bacteriochlorophyll-based reaction centres. Marine AAP communities are generally dominated by species belonging to the Roseobacter clade. For this reason, we used marine Roseobacter-related strain COL2P as a model organism to characterize its photosynthetic apparatus, level of pigmentation and expression of photosynthetic complexes. This strain contained functional photosynthetic reaction centres with bacteriochlorophyll a and spheroidenone as the main light-harvesting pigments, but the expression of the photosynthetic apparatus was significantly reduced when compared to truly photoautotrophic species. Moreover, the absence of peripheral light-harvesting complexes largely reduced its light-harvesting capacity. The size of the photosynthetic unit was limited to 35.4 +/- 1.0 BChl a molecules supplemented by the same number of spheroidenone molecules. The contribution of oxidative phosphorylation and photophosphorylation was analysed by respiration and fluorometric measurements. Our results indicate that even with a such reduced photosynthetic apparatus, photophosphorylation provides up to three times higher electron fluxes than aerobic respiration. These results suggest that light-derived energy can provide a substantial fraction of COL2P metabolic needs.

• MeSH
• aerobióza genetika   MeSH
• anaerobióza genetika   MeSH
• bakteriální geny MeSH
• bakteriální proteiny genetika   MeSH
• bakteriální RNA analýza   MeSH
• bakteriochlorofyl A genetika   MeSH
• bakteriochlorofyly genetika   MeSH
• fotofosforylace MeSH
• fotosyntetická reakční centra (proteinové komplexy) genetika   MeSH
• fotosyntéza * genetika   MeSH
• fylogeneze MeSH
• karotenoidy metabolismus   MeSH
• konjugace genetická MeSH
• messenger RNA analýza   MeSH
• mořská voda MeSH
• regulace genové exprese u bakterií MeSH
• Roseobacter genetika   metabolismus   MeSH
• sekvence aminokyselin MeSH
• spotřeba kyslíku genetika   MeSH
• světlo MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriální RNA MeSH
• bakteriochlorofyl A MeSH
• bakteriochlorofyly MeSH
• fotosyntetická reakční centra (proteinové komplexy) MeSH
• karotenoidy MeSH
• messenger RNA MeSH
• spheroidenone MeSH Prohlížeč