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Photosynthetic Electron Transport in an Anoxygenic Photosynthetic Bacterium Afifella (Rhodopseudomonas) marina Measured Using PAM Fluorometry
Author(s) -
Ritchie Raymond J.,
Runcie John W.
Publication year - 2013
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2012.01241.x
Subject(s) - anoxygenic photosynthesis , photosynthesis , quantum yield , electron transport chain , absorptance , photochemistry , analytical chemistry (journal) , chemistry , botany , photosynthetic reaction centre , fluorescence , biology , physics , optics , phototroph , environmental chemistry , reflectivity
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 ( BC hl a RC ‐2‐ LH 1) 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 = ( ETR max × E / E opt ) × exp(1 − E / E opt )). Maximum ETR ( ETR max ) was ≈1000–2000 μmol e − mg −1 BC hl 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 h λ −1 ; or ≈11.8 ± 2.9 mol e − mol h λ −1 m 2 μg −1 BC hl 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 ).