Identification of symbiosis-specific c-type cytochromes and a putative oxidase in bacteroids of Rhizobium leguminosarum biovar viciae

Abstract

Covalently bound haem proteins and cytochromes were analysed in Rhizobium leguminosamm biovar viciae free-living cells and nitrogen-f ixing bacteroids isolated from pea nodules. Increased levels of spectroscopically detectable cytochrome c in bacteroids were correlated with the appearance of two proteins of M, 30000 and 28000 that contained covalently bound haem. Conversely, bacteroids had undetectable levels of a periplasmic cytochrome c of M, 14000 that is normally present in free-living bacteria. Difference spectra confirmed that the terminal oxidases, cytochromes aa, and d, were absent, and photodissociation spectra revealed novel components that may be due to a bacteroid terminal oxidase.

A Cytochrome cbb 3 (Cytochrome c) Terminal Oxidase in Azospirillum brasilense Sp7 Supports Microaerobic Growth

“…The cytochrome cbb 3 cytochrome c oxidase, encoded by the fixNOQP operon in rhizobial species (18,23,32,38,50) or by a similar cco(cyt)NOQP operon in other bacteria (7,39,43,45), appears to be a cytochrome c terminal oxidase belonging to the heme-copper oxidase superfamily (14). In most rhizobial species this oxidase is essential for nitrogen-fixing endosymbiosis (18,32,50) and is characterized by an extremely high O 2 affinity (16,33). In the bacteria Magnetospirillum magnetoaceticum and Agrobacterium tumefaciens, and in Azorhizobium caulinodans growing nonsymbiotically, the cbb 3 -type cytochrome c terminal oxidase seems to be at least partially responsible for the microaerobic respiration (23,39,43).…”

Terminal oxidases of Azoarcus sp. BH72, a strictly respiratory diazotroph

“…Such an adaptation is crucial for nitrogen-fixing bacteria that have an aerobic type of metabolism. Different species of rhizobia use cytochrome c oxidase of the aa-s type as the dominant oxidase during aerobic growth [7,37,38]. Under microaerobic conditions, the alternative cytochrome c oxidase of the ebb' type is induced in rhizobia [10,11] as well as in R. sphaeroides [33] and in P. denitrificans [34].…”