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Effect of Carotenoid Biosynthesis Inhibition on the Chlorosome Organization in Chlorobium phaeobacteroides Strain CL1401
Author(s) -
Arellano Juan B.,
Psencik Jakub,
Borrego Carles M.,
Ma YingZhong,
Guyoneaud Rémy,
GarciaGil Jesús,
Gillbro Tomas
Publication year - 2000
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 - 10.1562/0031-8655(2000)0710715eocbio2.0.co2
Subject(s) - library science , ecology , geography , chemistry , biology , computer science
We have studied the effect of the absence of carotenoids on the organization of bacteriochlorophylls (BChls) in chlorosomes of Chlorobium ( Chl. ) phaeobacteroides strain CL1401. Carotenoid‐depleted chlorosomes were obtained by means of 2‐hydroxybiphenyl–supplemented cultures. In the presence of the inhibitor, isorenieratene (Isr) and β‐Isr biosynthesis were inhibited to more than 95%, leading to an accumulation of the colorless precursor phytoene inside the chlorosomes. In addition, there was a 30–40% decrease in the baseplate BChl a content. The absorption spectrum of the carotenoid‐depleted chlorosomes showed a 10 nm blue shift in the BChl e Q y absorption peak. Under reducing conditions, a decrease in the BChl a /BChl e fluorescence emission ratio was observed in carotenoid‐depleted chlorosomes relative to that in control chlorosomes, caused mainly by the decrease in the BChl a content. The steady‐state fluorescence emission anisotropy in the BChl e region dropped from ∼0.24 for native chlorosomes to ∼0.14 for carotenoid‐depleted ones, indicating reorganization of BChl e. The circular dichroism (CD) signal of the carotenoid‐depleted chlorosomes was increased two times in the BChl e Q y region. A simple model based on the structure proposed was used to explain the observed effects. Carotenoids might affect the angle between the direction of the BChl e Q y transition and the axis of the rod. The orientation of BChl a in the baseplate remains unchanged in carotenoid‐depleted chlorosomes, although there is a partial loss of BChl a as a consequence of a decrease in the baseplate size. The carotenoids are most likely rather close to the BChls and appear to be important for the aggregate structure in Chl. phaeobacteroides.