title: Photosynthetic electron transport in an anoxygenic photosynthetic bacterium Afifella (Rhodopseudomonas) marina measured using PAM fluorometry.
abstract: Blue diode-based pulse amplitude modulation (PAM) technology can be used to measure the photosynthetic electron transport rate (ETR) in a purple nonsulfur anoxygenic photobacterium, Afifella (Rhodopseudomonas) marina. Rhodopseudomonads have a reaction center light harvesting antenna complex containing an RC-2 type bacteriochlorophyll a protein (BChl a RC-2-LH1) which has a blue absorption peak and variable fluorescence similar to PSII. Absorptance of cells filtered onto glass fiber disks was measured using a blue-diode-based absorptance meter (Blue-RAT) so that absolute ETR could be calculated from PAM experiments. Maximum quantum yield (Y) was ≈0.6, decreasing exponentially as irradiance increased. ETR vs irradiance (P vs E) curves fitted the waiting-in-line model (ETR = (ETRmax  × E/Eopt ) × exp(1 - E/Eopt )). Maximum ETR (ETRmax ) was ≈1000-2000 μmol e(-)  mg(-1)  BChl a h(-1) . Fe(2+) , bisulfite and thiosulfate act as photosynthetic electron donors. Optimum irradiance was ≈100 μmol m(-2)  s(-1) PPFD even in Afifella grown in sunlight. Quantum efficiencies (α) were ≈0.3-0.4 mol e(-)  mol hλ(-1) ; or ≈11.8 ± 2.9 mol e(-)  mol hλ(-1)  m(2)  μg(-1)  BChl a). An underlying layer of Afifella in a constructed algal/photosynthetic bacterial mat has little effect on the measured ETR of the overlying oxyphotoautotroph (Chlorella).
authors.affiliation: Tropical Environmental Plant Biology Unit, Faculty of Technology and Environment, Prince of Songkla University, Phuket, Thailand. raymond.r@phuket.psu.ac.th
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Ritchie
authors.forename: John W
authors.initials: JW
authors.lastname: Runcie
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D025541:Bacteriochlorophyll A / Q000737:chemistry*; D002413:Cations, Divalent; D055664:Electrochemical Techniques; D004579:Electron Transport; D004583:Electrons; D005453:Fluorescence; D005470:Fluorometry / Q000379:methods; D007501:Iron / Q000737:chemistry; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects*; D012241:Rhodopseudomonas / Q000737:chemistry*; D013447:Sulfites / Q000737:chemistry; D013885:Thiosulfates / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; D002413:Cations, Divalent; D045342:Light-Harvesting Protein Complexes; D013447:Sulfites; D013885:Thiosulfates; D007501:Iron; C042345:hydrogen sulfite