Dataset Information

Picosecond kinetics of light harvesting and photoprotective quenching in wild-type and mutant phycobilisomes isolated from the cyanobacterium Synechocystis PCC 6803.

ABSTRACT: In high light conditions, cyanobacteria dissipate excess absorbed energy as heat in the light-harvesting phycobilisomes (PBs) to protect the photosynthetic system against photodamage. This process requires the binding of the red active form of the Orange Carotenoid Protein (OCP(r)), which can effectively quench the excited state of one of the allophycocyanin bilins. Recently, an in vitro reconstitution system was developed using isolated OCP and isolated PBs from Synechocystis PCC 6803. Here we have used spectrally resolved picosecond fluorescence to study wild-type and two mutated PBs. The results demonstrate that the quenching for all types of PBs takes place on an allophycocyanin bilin emitting at 660 nm (APC(Q)(660)) with a molecular quenching rate that is faster than (1 ps)(-1). Moreover, it is concluded that both the mechanism and the site of quenching are the same in vitro and in vivo. Thus, utilization of the in vitro system should make it possible in the future to elucidate whether the quenching is caused by charge transfer between APC(Q)(660) and OCP or by excitation energy transfer from APC(Q)(660) to the S(1) state of the carotenoid--a distinction that is very hard, if not impossible, to make in vivo.

SUBMITTER: Tian L

PROVIDER: S-EPMC3318131 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Picosecond kinetics of light harvesting and photoprotective quenching in wild-type and mutant phycobilisomes isolated from the cyanobacterium Synechocystis PCC 6803.

Tian Lijin L Gwizdala Michal M van Stokkum Ivo H M IH Koehorst Rob B M RB Kirilovsky Diana D van Amerongen Herbert H

Biophysical journal 20120403 7

In high light conditions, cyanobacteria dissipate excess absorbed energy as heat in the light-harvesting phycobilisomes (PBs) to protect the photosynthetic system against photodamage. This process requires the binding of the red active form of the Orange Carotenoid Protein (OCP(r)), which can effectively quench the excited state of one of the allophycocyanin bilins. Recently, an in vitro reconstitution system was developed using isolated OCP and isolated PBs from Synechocystis PCC 6803. Here we ...[more]

PMID: 22500770

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Project description:BackgroundCyanobacteria are phototrophic prokaryotes that convert inorganic carbon as CO2 into organic compounds at the expense of light energy. They need only inorganic nutrients and can be cultivated to high densities using non-arable land and seawater. This has made cyanobacteria attractive organisms for the production of biofuels and chemical feedstock. Synechocystis sp. PCC 6803 is one of the most widely used cyanobacterial model strains. Based on its available genome sequence and genetic tools, Synechocystis has been genetically modified to produce different biotechnological products. Efficient isoprene production is an attractive goal because this compound is widely used as chemical feedstock.ResultsHere, we report on our attempts to generate isoprene-producing strains of Synechocystis using a plasmid-based strategy. As previously reported, a codon-optimized plant isoprene synthase (IspS) was expressed under the control of different Synechocystis promoters that ensure strong constitutive or light-regulated ispS expression. The expression of the ispS gene was quantified by qPCR and Western blotting, while the amount of isoprene was quantified using GC-MS. In addition to isoprene measurements in the headspace of closed culture vessels, single photon ionization time-of-flight mass spectrometry (SPI-MS) was applied, which allowed online measurements of isoprene production in open-cultivation systems under various conditions. Under standard conditions, a good correlation existed between ispS expression and isoprene production rate. The cultivation of isoprene production strains under NaCl-supplemented conditions decreased isoprene production despite enhanced ispS mRNA levels. The characterization of the metabolome of isoprene-producing strains indicated that isoprene production might be limited by insufficient precursor levels. Transcriptomic analysis revealed the upregulation of mRNA and regulatory RNAs characteristic of acclimation to metabolic stress.ConclusionsOur best production strains produced twofold higher isoprene amounts in the presence of low NaCl concentrations than previously reported strains. These results will guide future attempts to establish isoprene production in cyanobacterial hosts.

Dataset Information

Picosecond kinetics of light harvesting and photoprotective quenching in wild-type and mutant phycobilisomes isolated from the cyanobacterium Synechocystis PCC 6803.

Publications

Picosecond kinetics of light harvesting and photoprotective quenching in wild-type and mutant phycobilisomes isolated from the cyanobacterium Synechocystis PCC 6803.

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