title: Artificially acquired chlorophyll b is highly acceptable to the thylakoid-lacking cyanobacterium, Gloeobacter violaceus PCC 7421.
abstract: Unicellular cyanobacterium Gloeobacter violaceus is an only known oxygenic photosynthetic organism that lacks thylakoid membrane. Molecular phylogenetic analyses indicate that G. violaceus is an early-branching cyanobacterium within cyanobacterial clade. Therefore, the photosynthetic system of G. violaceus is considered to be partly similar to that of the ancestral cyanobacteria that would lack thylakoid membrane. G. violaceus possesses chlorophyll (Chl) a as the only chlorophyll species like most cyanobacteria. It was proposed that the ancestral oxygenic photosynthetic organism had not only Chl a and phycobilins but also Chl b. However, no organism which contains both Chl a and Chl b and lacks thylakoid membrane has been found in nature. Therefore, we introduced the chlorophyllide a oxygenase gene responsible for Chl b biosynthesis into G. violaceus. In the resultant transformant, Chl b accumulated at approximately 11% of total Chl independent of growth phase. Photosystem I complexes isolated from the transformant contained Chl b at 9.9% of total Chl. The presence of Chl b in the photosystem I complexes did not inhibit trimer formation. Furthermore, time-resolved fluorescence spectrum demonstrated that Chl b transferred energy to Chl a in the photosystem I complexes and did not disturb the energy transfer among the Chl a molecules. These results show that G. violaceus is tolerant to artificially produced Chl b and suggest the flexibility of photosystem for Chl composition in the ancestral oxygenic photosynthetic organism.
authors: Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan.
authors: Mie
authors: M
authors: Araki
authors: Molecular Photoscience Research Center, Kobe University, Kobe, 657-8501, Japan; Japan Science and Technology Agency, CREST, Kobe 657-8501, Japan.
authors: Seiji
authors: S
authors: Akimoto
authors: Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan.
authors: Mamoru
authors: M
authors: Mimuro
authors: Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan; Graduate School of Global Environmental Studies, Kyoto University, Kyoto 606-8501, Japan. Electronic address: tsuchiya.toru.8e@kyoto-u.ac.jp.
authors: Tohru
authors: T
authors: Tsuchiya
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002734:Chlorophyll / Q000235:genetics*; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D048928:Prochlorophytes / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D010105:Oxygenases; C115272:chlorophyll a oxygenase; D000077194:Chlorophyll A
keywords: Chlorophyll b; Chlorophyllide a oxygenase; Cyanobacteria; Gloeobacter violaceus; Photosystem I; Time-resolved fluorescence spectra