The ordered macromolecular surface of polyester inclusion bodies inPseudomonas oleovotans

Abstract

Intracellular inclusion bodies of poly(β-hydroxyalkanoates) (PHAs) have been studied in various microorganisms since Lemoigne's discovery of PHAs in 1925. Recently, the research in several laboratories, including our own, has addressed the role of proteins, lipids, and water associated with these accumulations. Our research has examined the boundary of polymer inclusion bodies. Electron microscopy demonstrated that the polymer is encompassed by two paracrystalline arrays. SDS-PAGE, Western blot, or immunogold labelling demonstrated that both contain a 43-kDa protein as a major component. Immunogold labelling also demonstrated that 55- and 59-kDa proteins are located, exclusively, on the array associated with the accumulating polymer. Results from microelemental analysis and preliminary thin-layer chromatography of released lipids were consistent with the suggestion that phospholipids also had a role in this organized assembly. A model has been suggested, aimed at focusing attention on this organized boundary region. It is consistent with maintenance of the amorphous state of the polymer both intracellularly and after isolation, provides sites for biosynthetic and degradative enzymes, and accounts for the polyester, protein, and lipid components known to be present. Interestingly, the anti-43-kDa antibody also recognized a 43-kDa species released from the outer surface of this microbe. The research presented here and the model developed from it, suggest that microbial synthesis, containment, and degradation of polyester are carried out in association with a highly organized and complex intracellular assembly that may provide, within the bacterial cytosol, a unique microenvironment for biochemical activities.Key words: polyester, inclusion granule, Pseudomonas oleovorans.