Isolation and purification of granule-associated proteins relevant for poly(3-hydroxybutyric acid) biosynthesis from methylotrophic bacteria relying on the serine pathway

The poly(3-hydroxybutyric acid) (PHB) granules from eight methylotrophic bacteria that use the serine pathway were isolated in a sucrose gradient (1–2 M); these bacteria included members of the genus Methylobacterium, Mycoplana rubra, and PHB-leaky mutants of Methylobacterium rhodesianum. As shown by sodium dodecyl sulfate – polyacrylamide gel electrophoresis, the granules from all investigated methylotrophic strains revealed two major bands representing small proteins. An efficient purification procedure for these two low molecular weight proteins associated with the PHB granules was developed by solubilization of the proteins with Triton X-114 and affinity chromatography on Procion Blue-H-ERD.