Intracellular degradation of poly(3-hydroxybutyric acid) accumulated by Azotobacter chroococcum MAL-201.
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.
Saha
Soma Pal
SP
University of Calcutta, Departament of Botany, India.
Paul
A K
AK
D001395:Azotobacter / Q000254:growth & development / Q000378:metabolism*; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D006885:Hydroxybutyrates / Q000378:metabolism*; D011091:Polyesters / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
D003470:Culture Media; D006885:Hydroxybutyrates; D011091:Polyesters; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates