Rearrangement of light harvesting bacteriochlorophyll homologues as a response of green sulfur bacteria to low light intensities |
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Authors: | C M Borrego L J Garcia-Gil |
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Institution: | (1) Laboratory of Microbiology, Department of Biology, University of Girona, Hospital 6, E-17071 Girona, Spain;(2) Institute of Aquatic Ecology, University of Girona, Hospital 6, E-17071 Girona, Spain |
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Abstract: | The pigment composition of two species of green-colored BChl c-containing green sulfur bacteria (Chlorobium limicola and C. chlorovibrioides) and two species of brown-colored BChl e-containing ones (C. phaeobacteroides and C. phaeovibrioides) incubated at different light intensities have been studied. All species responded to the reduction of light intensity from 50 to 1 Einstein(E) m–2 s–1 by an increase in the specific content of light harvesting pigments, bacteriochlorophylls and carotenoids. At critical light intensities (0.5 to 0.1 E m–2 s–1) only brown-colored chlorobia were able to grow, though at low specific rates (0.002 days–1 mg prot–1). High variations in the relative content of farnesyl-bacteriochlorophyll homologues were found, in particular BChl e
1 and BChl e
4, which were tentatively identified as M, E] and I, E] BChlF
e, respectively. The former was almost completely lost upon reduction of light intensity from 50 to 0.1 E m–2 s–1, whereas the latter increased from 7.2 to 38.4% and from 13.6 to 42.0% in C. phaeobacteroides and C. phaeovibrioides, respectively. This increase in the content of highly alkylated pigment molecules inside the chlorosomes of brown species is interpreted as a physiological mechanism to improve the efficiency of energy transfer towards the reaction center. This study provides some clues for understanding the physiological basis of the adaptation of brown species to extremely low light intensities.Abbreviations BChl
bacteriochlorophyll
- M, E] BChlF
e
8-methyl, 12-ethyl BChl e, esterified with farnesol (F). Analogously: I - isobutyl
- Pr
propyl
- Car
carotenoids
- Chlb
chlorobactene
- HPLC
high performance liquid chromatography
- Isr
isorenieratene
- LHP
light harvesting pigments
- PDA
photodiode array detector
- RC
reaction center
- RCH
relative content of homologues |
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Keywords: | bacteriochlorophyll homologues Chlorobium light adaptation light harvesting pigments energy transfer |
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