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Stereochemical conversion of C 3‐vinyl group to 1‐hydroxyethyl group in bacteriochlorophyll c by the hydratases BchF and BchV : adaptation of green sulfur bacteria to limited‐light environments
Author(s) -
Harada Jiro,
Teramura Misato,
Mizoguchi Tadashi,
Tsukatani Yusuke,
Yamamoto Ken,
Tamiaki Hitoshi
Publication year - 2015
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13208
Subject(s) - chlorosome , green sulfur bacteria , biology , bacteriochlorophyll , mutant , sulfur , bacteria , stereochemistry , pigment , biochemistry , photosynthesis , gene , chemistry , genetics , organic chemistry
Summary Photosynthetic green sulfur bacteria inhabit anaerobic environments with very low‐light conditions. To adapt to such environments, these bacteria have evolved efficient light‐harvesting antenna complexes called as chlorosomes, which comprise self‐aggregated bacteriochlorophyll c in the model green sulfur, bacterium C hlorobaculum tepidum . The pigment possess a hydroxy group at the C 3 1 position that produces a chiral center with R ‐ or S ‐stereochemistry and the C 3 1 ‐hydroxy group serves as a connecting moiety for the self‐aggregation. C hlorobaculum tepidum carries the two possible homologous genes for C 3‐vinyl hydratase, bch F and bch V . In the present study, we constructed deletion mutants of each of these genes. Pigment analyses of the bch F ‐inactivated mutant, which still has BchV as a sole hydratase, showed higher ratios of S ‐epimeric bacteriochlorophyll c than the wild‐type strain. The heightened prevalence of S ‐stereoisomers in the mutant was more remarkable at lower light intensities and caused a red shift of the chlorosomal Q y absorption band leading to advantages for light‐energy transfer. In contrast, the bch V ‐mutant possessing only BchF showed a significant decrease of the S ‐epimers and accumulations of C 3‐vinyl BC hl c species. As trans‐ criptional level of bch V was upregulated at lower light intensity, the C hlorobaculum tepidum adapted to low‐light environments by control of the bch V transcription.