Rhizobium phaseoli cytochrome c‐deficient mutant induces empty nodules on Phaseolus vulgaris L.

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Abstract
A Rhizobium phaseoli cytochrome mutant, unable to oxidize N,N,N′,N′ ‐tetramethyl‐p‐phenylend(amine (TMPD), was isolated after Mu‐dl (Kan lac) mutagenesis of the wild‐type strain CE‐3. Mutant strain CFN4202 had sixfold less haem‐c but similar levels of b type, o and aa3 cytochromes than the wild‐type strain. CFN402 strain also showed reduced NADH‐ and TMPD‐oxidase activity than the wild‐type strain. Succinate‐oxidase activities were very similar. Western blot experiments, using antiserum against bovine c1 and c cytochromes, revealed that both proteins were present in CFN4202 membranes, suggesting a defect of haem binding to cytochrome c. Nodules formed by this strain in Phaseolus vulgaris did not contain bacteroids. These data suggest that the cytochrome c‐aa3 chain or some other respiratory chain, containing c‐type cytochromes in R. phaseoli, is essential for bacterial division during the early steps of the symbiotic interaction with the legume‐host.