title: Selective repression of light harvesting complex 2 formation in Rhodobacter azotoformans by light under semiaerobic conditions.
abstract: Photosystem formation in anaerobic anoxygenic phototrophic bacteria (APB) is repressed by oxygen but is de-repressed when oxygen tension decreases. Under semiaerobic conditions, the synthesis of photopigments and pigment protein complexes in Rhodobacter (Rba.) sphaeroides are repressed by light. AppA, a blue-light receptor, mediates this regulation. In the present study, it was showed that the synthesis of bacteriochlorophyll, carotenoid, and pigment protein complexes in Rba. azotoformans 134K20 was significantly repressed by oxygen. Oxygen exposure also led to a conversion of spheroidene to spheroidenone. In semiaerobically growing cells, light irradiation resulted in a decrease in the formation of photosystem, and blue light was found to be the most effective light source. Blue light reduced the contents of bacteriochlorophyll and carotenoid slightly, but had negligible effects on light harvesting complex (LH) 1 content, whereas the content of LH2 was significantly decreased indicating that blue light selectively repressed the synthesis of LH2 in semiaerobically growing 134K20. It was concluded that, similar to Rba. sphaeroides, a blue light receptor presented in strain 134K20 played important roles in its light-dependent repression. A possible mechanism involved in controlling the differential inhibitory of blue light on the synthesis of photosystem was discussed.
authors.affiliation: Department of Bioengineering and Biotechnology, Huaqiao University, Xiamen, 361021, P. R. China.
authors.forename: Huiying
authors.initials: H
authors.lastname: Yue
authors.affiliation: Department of Bioengineering and Biotechnology, Huaqiao University, Xiamen, 361021, P. R. China.
authors.forename: Chungui
authors.initials: C
authors.lastname: Zhao
authors.affiliation: Department of Bioengineering and Biotechnology, Huaqiao University, Xiamen, 361021, P. R. China.
authors.forename: Kai
authors.initials: K
authors.lastname: Li
authors.affiliation: Department of Bioengineering and Biotechnology, Huaqiao University, Xiamen, 361021, P. R. China.
authors.forename: Suping
authors.initials: S
authors.lastname: Yang
mesh_terms: D001429:Bacteriochlorophylls / Q000096:biosynthesis; D002338:Carotenoids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000502:physiology* / Q000528:radiation effects; D016992:Rhodobacter / Q000502:physiology* / Q000528:radiation effects; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000502:physiology
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; C104880:spheroidenone; D002338:Carotenoids
keywords: Light; Light harvesting complex 1; Repression