title: Effect of carotenoid biosynthesis inhibition on the chlorosome organization in Chlorobium phaeobacteroides strain CL1401.
abstract: 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 beta-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 Qy 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 approximately 0.24 for native chlorosomes to approximately 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 Qy 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 Qy 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.
authors.affiliation: Laboratory of Microbiology, Institute of Aquatic Ecology, University of Girona, Spain. juan@morgat.udg.es
authors.forename: J B
authors.initials: JB
authors.lastname: Arellano
authors.forename: J
authors.initials: J
authors.lastname: Psencik
authors.forename: C M
authors.initials: CM
authors.lastname: Borrego
authors.forename: Y Z
authors.initials: YZ
authors.lastname: Ma
authors.forename: R
authors.initials: R
authors.lastname: Guyoneaud
authors.forename: J
authors.initials: J
authors.lastname: Garcia-Gil
authors.forename: T
authors.initials: T
authors.lastname: Gillbro
mesh_terms: D002338:Carotenoids / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D019414:Chlorobi / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D013050:Spectrometry, Fluorescence
chemical_list: D002338:Carotenoids