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Title: Assembly of functional photosystem complexes in Rhodobacter sphaeroides incorporating carotenoids from the spirilloxanthin pathway

Carotenoids protect the photosynthetic apparatus against harmful radicals arising from the presence of both light and oxygen. They also act as accessory pigments for harvesting solar energy, and are required for stable assembly of many light-harvesting complexes. In the phototrophic bacterium Rhodobacter (Rba.) sphaeroides phytoene desaturase (CrtI) catalyses three sequential desaturations of the colourless carotenoid phytoene, extending the number of conjugated carbon-carbon double bonds, N, from three to nine and producing the yellow carotenoid neurosporene; subsequent modifications produce the yellow/red carotenoids spheroidene/spheroidenone (N=10/11). Genomic crtI replacements were used to swap the native three-step Rba. sphaeroides CrtI for the four-step Pantoea agglomerans enzyme, which re-routed carotenoid biosynthesis and culminated in the production of 2,2'-diketo-spirilloxanthin under semi-aerobic conditions. The new carotenoid pathway was elucidated using a combination of HPLC and mass spectrometry. Premature termination of this new pathway by inactivating crtC or crtD produced strains with lycopene or rhodopin as major carotenoids. All of the spirilloxanthin series carotenoids are accepted by the assembly pathways for LH2 and RC-LH1-PufX complexes. The efficiency of carotenoid-to-bacteriochlorophyll energy transfer for 2,2'-diketo-spirilloxanthin (15 conjugated CC bonds; N=15) in LH2 complexes is low, at 35%. High energy transfer efficiencies were obtained for neurosporene (N=9; 94%), spheroidene (N=10; 96%)more » and spheroidenone (N=11; 95%), whereas intermediate values were measured for lycopene (N=11; 64%), rhodopin (N=11; 62%) and spirilloxanthin (N=13; 39%). In conclusion, the variety and stability of these novel Rba. sphaeroides antenna complexes make them useful experimental models for investigating the energy transfer dynamics of carotenoids in bacterial photosynthesis.« less
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  1. Univ. of Sheffield (United Kingdom). Dept. of Molecular Biology and Biotechnology
  2. Washington Univ., St. Louis, MO (United States). Dept. of Chemistry
  3. Washington Univ., St. Louis, MO (United States). Photosynthetic Antenna Research Center
  4. Washington Univ., St. Louis, MO (United States). Photosynthetic Antenna Research Cente
  5. Univ. of Sheffield (United Kingdom). Dept. of Molecular Biology and Biotechnology; Univ. of Sheffield (United Kingdom). ChELSI Inst., Dept. of Chemical and Biological Engineering
  6. China Agricultural Univ., Beijing (China). Dept. of Microbiology and Immunology
Publication Date:
OSTI Identifier:
Grant/Contract Number:
SC0001035; 8P41GM103422-35; EP/I012060/1; BB/G021546/1; 338895
Published Article
Journal Name:
Biochimica et Biophysica Acta - Bioenergetics
Additional Journal Information:
Journal Volume: 1847; Journal Issue: 2; Journal ID: ISSN 0005-2728
Research Org:
Energy Frontier Research Centers (EFRC). Photosynthetic Antenna Research Center (PARC)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Orgs:
PARC partners with Washington University in St. Louis (lead); University of California, Riverside; University of Glasgow, UK; Los Alamos National Laboratory; University of New Mexico; New Mexico Corsortium; North Carolina State University; Northwestern University; Oak Ridge National Laboratory; University of Pennsylvania; Sandia National Laboratories; University of Sheffield, UK
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; solar (fuels); photosynthesis (natural and artificial); biofuels (including algae and biomass); bio-inspired; charge transport; membrane; synthesis (novel materials); synthesis (self-assembly); Bacterial photosynthesis; Light harvesting; Carotenoid; Membrane protein; Antenna; Synthetic biology