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Journal of Bacteriology, October 2000, p. 5440-5447, Vol. 182, No. 19
Department of Microbiology and Immunology, University of
British Columbia, Vancouver, British Columbia,
Canada,1 and ExxonMobil Research and
Engineering Company, Annandale, New Jersey2
Received 26 April 2000/Accepted 10 July 2000
The orf162b sequence, the second open reading frame 3'
of the reaction center (RC) H protein gene puhA in the
Rhodobacter capsulatus photosynthesis gene cluster, is
shown to be transcribed from a promoter located 5' of puhA.
A nonpolar mutation of orf162b was generated by replacing
most of the coding region with an antibiotic resistance cartridge.
Although the mutant strain initiated rapid photosynthetic growth,
growth slowed progressively and cultures often entered a
pseudostationary phase. The amounts of the RC and light harvesting
complex I (LHI) in cells obtained from such photosynthetic cultures
were abnormally low, but these deficiencies were less severe when the
mutant was grown to a pseudostationary phase induced by low aeration in
the absence of illumination. The orf162b mutation did not
significantly affect the expression of a
pufB::lacZ translationally in-frame
gene fusion under the control of the puf promoter,
indicating normal transcription and translation of RC and LHI genes.
Spontaneous secondary mutations in the strain with the
orf162b disruption resulted in a bypass of the
photosynthetic growth retardation and reduced the level of light
harvesting complex II. These results and the presence of sequences
similar to orf162b in other species indicate that the
Orf162b protein is required for normal levels of the photosynthetic apparatus in purple photosynthetic bacteria.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The orf162b Sequence of
Rhodobacter capsulatus Encodes a Protein Required for
Optimal Levels of Photosynthetic Pigment-Protein Complexes
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, University of British Columbia, 300 - 6174 University Blvd., Vancouver, British Columbia, Canada V6T 1Z3. Phone: (604) 822-6896. Fax: (604) 822-6041. E-mail:
jbeatty{at}interchange.ubc.ca.
Journal of Bacteriology, October 2000, p. 5440-5447, Vol. 182, No. 19
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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