CHARACTERIZATION OF A 14-KDA COMPONENT WITH LOW EXPRESSION IN A UNIQUE NOD(-) BRADYRHIZOBIUM-JAPONICUM() FIX()

A pronase-sensitive, 14 kDa component of bacteroids of Bradyrhizobium japonicum I-110ARS was identified and characterized using monoclonal a ntibodies. This component was weakly synthesized or was missing in bac teroids of a unique Nod(+) Fix(-) mutant. ARS2525. Both the 14 kDa com ponent and poly-beta-hydroxybutyrate (PHB) were located in the same pr otein peak after sucrose density gradient separation of lysed bacteroi ds. Thirty-five-day-old bacteroids of B. japonicum I-110ARS contained up to 10 times more PHB than B. japonicum ARS2525 bacteroids. Immunocy tochemistry of ultra-thin nodule sections showed that the component wa s associated with PHB granules in the bacteroids, possibly with the li miting membrane around the granules. This observation implies that the component may be similar to other storage-lipid body proteins. Whethe r low synthesis of the 14 kDa component or low PHB content was a cause , a consequence or,related to the Fix(-) phenotype was not established .