Combining retinal-based and chlorophyll-based (oxygenic) photosynthesis : Proteorhodopsin expression increases growth rate and fitness of a Delta PSI strain of Synechocystis sp. PCC6803

• To fill the "green absorption gap", a green absorbing proteorhodopsin was expressed in a PSI-deletion strain (Delta PSI) of Synechocystis sp. PCC6803. Growth-rate measurements, competition experiments and physiological characterization of the proteorhodopsin-expressing strains, relative to the Delta PSI control strain, allow us to conclude that proteorhodopsin can enhance the rate of photoheterotrophic growth of Delta PSI Synechocystis strain. The physiological characterization included measurement of the amount of residual glucose in the spent medium and analysis of oxygen uptake- and production rates. To explore the use of solar radiation beyond the PAR region, a red-shifted variant Proteorhodopsin-D212N/F234S was expressed in a retinal-deficient PSI-deletion strain (Delta PSI/Delta SynACO). Via exogenous addition of retinal analogue an infrared absorbing pigment (maximally at 740 nm) was reconstituted in vivo. However, upon illumination with 746 nm light, it did not significantly stimulate the growth (rate) of this mutant. The inability of the proteorhodopsin-expressing Delta PSI strain to grow photoautotrophically is most likely due to a kinetic rather than a thermodynamic limitation of its NADPH-dehydrogenase in NADP(+)-reduction.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Nyckelord

Retinal-based proton pump

PSI-deletion

Synechocystis

Oxygen evolution

Glucose consumption

Growth stimulation

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