Effect of carotenoid deficiency on cells and chlorosomes of Chlorobium phaeobacteroides.
The effects of inhibition of carotenoid biosynthesis by 2-hydroxybiphenyl on the photosynthetic growth, pigment composition and chlorosome structure of Chlorobium phaeobacteroides strain CL1401 were examined. At a concentration of 20 micrograms 2-hydroxybiphenyl .ml-1, carotenoid synthesis was largely inhibited (85%), but the photosynthetic growth rate was almost unaffected (mu control = 0.00525 +/- 0.00007 h-1 and mu HBP-treated = 0.00505 +/- 0.0005 h-1). Cells grown in the presence of the inhibitor were 5 microns-70 microns long, while control cells were between 2-5 microns long. Moreover, 2-hydroxybiphenyl-treated cells contained fewer, unevenly distributed chlorosomes per micron of cytoplasmic membrane with an irregular arrangement (2.5 +/- 1.5 vs of 9.1 +/- 1.9). This was concomitant to the 83% decrease in the content of bacteriochlorophyll (BChl) e in 2-hydroxybiphenyl-treated cells. Electron microscopy revealed that the shape of carotenoid-depleted chlorosomes changed from ellipsoidal to spherical, although the mean volume was similar to that of control chlorosomes. SDS-PAGE analysis of the chlorosome polypeptide composition showed that the amount of CsmA protein decreased by 60% in carotenoid-depleted chlorosomes. This was paralleled by a decrease in the baseplate BChl a content. The data suggest that carotenoids are close to the chlorosomal baseplate, where they carry out both structural and photoprotective functions.
Arellano
J B
JB
Laboratory of Microbiology, Institute of Aquatic Ecology and Department of Biology, University of Girona, 17071, Girona, Spain.
Borrego
C M
CM
Martínez-Planells
A
A
Garcia-Gil
L J
LJ
D001713:Biphenyl Compounds / Q000494:pharmacology; D002338:Carotenoids / Q000502:physiology*; D019414:Chlorobi / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*; D010455:Peptides / Q000032:analysis; D010860:Pigments, Biological / Q000032:analysis
D001713:Biphenyl Compounds; D010455:Peptides; D010860:Pigments, Biological; D002338:Carotenoids; C004369:2-phenylphenol