Effect of light and oxygen and adaptation to changing light conditions in a photosynthetic mutant in which the LHII complex of Rhv. sulfidophilum was heterologously expressed in a strain of Rb. capsulatus whose puc operon was deleted.
In this paper we show the effect of oxygen and light on the expression of the photosynthetic apparatus of a mutant heterologously expressing the puc operon. This mutant was obtained by introducing in trans an expression plasmid, bearing the puc A, B, and C genes of Rhv. sulfidophilum, as well as its own promoter, in an LHII(-) mutant of Rb. capsulatus. The results showed that oxygen and light repressed LHII expression. Even low-light intensities lowered the LHII content to undetectable levels by spectrophotometry or by SDS-PAGE. In high-light grown cells, where the relative ratios of LHI and LHII complexes were significantly diminished, we were able to detect LHII complexes. Under the latter condition, the absorption spectrum showed that some pigment accumulated in the membrane even in the absence of cell division. These pigments were used in a later step to assemble LHII complexes, when the high-light grown cells were transferred to semiaerobiosis in the dark. Transition of high-light grown cells to low-light conditions allowed us to study the adaptability of these heterologous mutant cells. We observed that adaptation never occurred, in part probably owing to energy limitation.
Cátedra de Microbiología, Facultad de Agronomía, UBA and Instituto de Investigaciones Bioquímicas y Fisiológicas (IBYF-CONICET), Av. San Martín 4453, C1417 DSE, Ciudad Autónoma de Buenos Aires, Argentina.
María del Rosario
Mdel R
Barbieri Md
Norma L
NL
Kerber
Norma L
NL
Pucheu
Monier H
MH
Tadros
Augusto F
AF
García
D000222:Adaptation, Physiological; D020561:Alphaproteobacteria / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects*; D001426:Bacterial Proteins; D017353:Gene Deletion; D015870:Gene Expression; D005798:Genes, Bacterial; D008027:Light; D045342:Light-Harvesting Protein Complexes; D009154:Mutation; D009876:Operon; D010100:Oxygen; D010766:Phosphorylation; D010788:Photosynthesis / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D016354:Rhodobacter capsulatus / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects*
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; C023693:protein complex B800-850, Rhodobacter; D010100:Oxygen