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

ABSTRACT: 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%) and spheroidenone (N=11; 95%), whereas intermediate values were measured for lycopene (N=11; 64%), rhodopin (N=11; 62%) and spirilloxanthin (N=13; 39%). 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.

SUBMITTER: Chi SC

PROVIDER: S-EPMC4331045 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature

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

Chi Shuang C SC Mothersole David J DJ Dilbeck Preston P Niedzwiedzki Dariusz M DM Zhang Hao H Qian Pu P Vasilev Cvetelin C Grayson Katie J KJ Jackson Philip J PJ Martin Elizabeth C EC Li Ying Y Holten Dewey D Neil Hunter C C

Biochimica et biophysica acta 20141027 2

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, fr ...[more]

PMID: 25449968

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Project description:The flagellar lipoprotein FlgP has been identified in several species of bacteria, and its absence provokes different phenotypes. In this study, we show that in the alphaproteobacterium Rhodobacter sphaeroides, a ΔflgP mutant is unable to assemble the hook and the filament. In contrast, the membrane/supramembrane (MS) ring and the flagellar rod appear to be assembled. In the absence of FlgP a severe defect in the transition from rod to hook polymerization occurs. In agreement with this idea, we noticed a reduction in the amount of intracellular flagellin and the chemotactic protein CheY4, both encoded by genes dependent on σ28 This suggests that in the absence of flgP the switch to export the anti-sigma factor, FlgM, does not occur. The presence of FlgP was detected by Western blot in samples of isolated wild-type filament basal bodies, indicating that FlgP is an integral part of the flagellar structure. In this regard, we show that FlgP interacts with FlgH and FlgT, indicating that FlgP should be localized closely to the L and H rings. We propose that FlgP could affect the architecture of the L ring, which has been recently identified to be responsible for the rod-hook transition.IMPORTANCE Flagellar based motility confers a selective advantage on bacteria by allowing migration to favorable environments or in pathogenic species to reach the optimal niche for colonization. The flagellar structure has been well established in Salmonella However, other accessory components have been identified in other species. Many of these have been implied in adapting the flagellar function to enable faster rotation, or higher torque. FlgP has been proposed to be the main component of the basal disk located underlying the outer membrane in Campylobacter jejuni and Vibrio fischeri Its role is still unclear, and its absence impacts motility differently in different species. The study of these new components will bring a better understanding of the evolution of this complex organelle.

Dataset Information

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

Publications

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

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