Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/1995
Publication Date: N/A
Interpretive Summary: Cytochromes are proteins in living organisms that participate in the conversion of food into chemical energy that is used by all living cells for supporting the synthetic reactions of the cell. There are a diverse array of cytochromes produced by cells and the function of some of them is s unknown. Determining their function in symbiotic microorganisms will hel elucidate how these organisms provide energy for symbiotic nitrogen fixation. This paper describes the cloning of genes for three cytochromes of Bradyrhizobium japonicum, the symbiont of soybeans, and shows that one of the cytochromes is essential for anaerobic respiration. This knowledge is useful for scientists who are working to improve symbiotic nitrogen fixation in soybean.
Technical Abstract: Bradyrhizobium japonicum possesses three soluble c-type cytochromes, C550, C552, and C555. The genes for cytochromes C552 (cycC) were characterized previously. We report the cloning, sequencing and mutational analysis of the cytochrome C550 gene (cycA). A B. japonicum mutant with an insertion 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.