Characterization of a 14 kDa component with low expression in a unique Nod+ Fix- Bradyrhizobium japonicum

Abstract

A pronase-sensitive, 14 kDa component of bacteroids of Bradyrhizobium japonicum 1-1 IOARS was identified and characterized using monoclonal antibodies. This component was weakly synthesized or was missing in bacteroids of a unique Nod+ Fix-mutant, ARS2525. Both the 14 kDa component and poly-/?-hydroxybutyrate (PHB) were located in the same protein peak after sucrose density gradient separation of lysed bacteroids. Thirty-f ive-day-old bacteroids of B. japonicum I-11OARS contained up to 10 times more PHB than B. japonicum ARS2525 bacteroids. lmmunocytochemistry of ultra-thin nodule sections showed that the component was associated with PHB granules in the bacteroids, possibly with the limiting membrane around the granules. This observation implies that the component may be similar to other storage lipid body proteins. Whether 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.

Electron microscopic observations on the macromolecular organization of the boundary layer of bacterial PHA inclusion bodies.

“…However, it seems that the key enzyme of PHA biosynthesis is not the major protein component at the surface of the granules. When isolated PHA granules are subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis, the electropherograms revealed low molecularweight proteins as the predominant protein species in almost all PHA-accumulating bacteria (7,12,14,19,25,26). Based on the amino-acid sequence data of phasin molecules, models of the structure and composition of the PHA granule surface in Rhodococcus ruber and for the anchoring of the phasin (the GA 14 protein) monomer in a phospholipid monolayer were postulated (15).…”