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

Covalently bound haem proteins and cytochromes were analysed in Rhizobium leguminosarum biovar viciae free-living cells and nitrogen-fixing bacteroids isolated from pea nodules. Increased levels of spectroscopically detectable cytochrome c in bacteroids were correlated with the appearance of two proteins of Mr 30000 and 28000 that contained covalently bound haem. Conversely, bacteroids had undetectable levels of a periplasmic cytochrome c of M r 14000 that is normally present in free-living bacteria. Difference spectra confirmed that the terminal oxidases, cytochromes aa 3 and d, were absent, and photodissociation spectra revealed novel components that may be due to a bacteroid terminal oxidase.