title: Intracellular degradation of poly(3-hydroxybutyric acid) accumulated by Azotobacter chroococcum MAL-201.
abstract: Azotobacter chroococcum MAL-201 accumulates poly(3-hydroxybutyric acid) [P(3HB)] accounting 69% of cell dry weight (CDW) from glucose during growth in nitrogen-free Stockdale medium. Degradation of the accumulated polymer by the organism was studied under carbon-free medium following two-step cultivation method. P(3HB) content of cells decreased rapidly from 69% to 4.8% of CDW after 35 h under carbon-deprived condition. Autodigestion of P(3HB) was evident from the estimation of intracellular P(3HB) depolymerase (i-depolymerase) activity in cell-free extract using artificial P(3HB) granules as substrate. Polymer content decreased rapidly along with the increase in i-depolymerase activity and rate of polymer degradation when medium was supplemented with (NH4)2SO4 at 0.1% (w/v) level. However, the effects were reverse when organic nitrogenous substrate, beef extract at similar concentration was present in the medium. The optimum temperature and pH for i-depolymerase activity were 35 degrees C and 7.7 respectively. The oxygen-limiting condition (culture volume per flask volume, 50%) decreased 10.7% activity of i-depolymerase over control resulting a slow P(3HB) degradation. The presence of NaCl (6 x 10(3) microg/ml) showed a positive effect on i-depolymerase whereas EDTA (40 microg/ml) resulted in 20% less activity. Furthermore, the intracellular degradation of P(3HB) decreased the intrinsic viscosity, molecular weight and tensile strength of the accumulated polymer.
authors.affiliation: University of Calcutta, Departament of Botany, India.
authors.forename: Soma Pal
authors.initials: SP
authors.lastname: Saha
authors.forename: A K
authors.initials: AK
authors.lastname: Paul
mesh_terms: D001395:Azotobacter / Q000254:growth & development / Q000378:metabolism*; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D006885:Hydroxybutyrates / Q000378:metabolism*; D011091:Polyesters / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
chemical_list: D003470:Culture Media; D006885:Hydroxybutyrates; D011091:Polyesters; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates