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J. Bacteriol., Apr 1995, 2214-2217, Vol 177, No. 8
M Bott, L Thony-Meyer, H Loferer, S Rossbach, RE Tully, D Keister, CA Appleby and H Hennecke
Bradyrhizobium japonicum possesses three soluble c-type cytochromes, c550,
c552, and c555. The genes for cytochromes c552 (cycB) and c555 (cycC) were
characterized previously. Here we report the cloning, sequencing, and
mutational analysis of the cytochrome c550 gene (cycA). A B. japonicum
mutant with an insertion in cycA failed to synthesize a 12-kDa c-type
cytochrome. This protein was detectable in the cycA mutant complemented
with cloned cycA, which proves that it is the cycA gene product. The cycA
mutant, a cycB-cycC double mutant, and a cycA- cycB-cycC triple mutant
elicited N2-fixing root nodules on soybean (Nod+ Fix+ phenotype); hence,
none of these three cytochromes c is essential for respiration supporting
symbiotic N2 fixation. However, cytochrome c550, in contrast to cytochromes
c552 and c555, was shown to be essential for anaerobic growth of B.
japonicum, using nitrate as the terminal electron acceptor.
Copyright © 1995, American Society for Microbiology
Bradyrhizobium japonicum cytochrome c550 is required for nitrate respiration but not for symbiotic nitrogen fixation
Mikrobiologisches Institut, Eidgenossische Technische Hochschule, Zurich, Switzerland.
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