DIFFERENTIAL SCANNING CALORIMETRIC STUDY OF POLY(3-HYDROXYOCTANOATE) INCLUSIONS IN BACTERIAL-CELLS

Medium chain length polyhydroxyalkanoates, MCL-PHAs, produced by bacte ria as inclusion bodies or granules were analyzed in situ by different ial scanning calorimetry (DSC) without isolation from the cells. The k inetic DSC study of PHA granules, which contained mostly 3-hydroxyocta noate units (PHO), in Pseudomonas putida BM01 cells showed that the po lymer within the granules existed in an amorphous state, but it crysta llized after dehydration of the cells under freeze-drying condition (b elow -50 degrees C) followed by annealing at ambient temperature. In t his manner, PHO within the cells readily crystallized to the maximum d egree of crystallinity within 24 h at room temperature, which was much faster than for the same polymer isolated by solvent extraction. This observation suggests that the polymer within the cellular granules ma y be well organized. The DSC endothermic melting peak areas for the ro om-temperature annealed polymers within the cells were directly propor tional to the amount of polymer in the cell, and the results from this type of quantitative analysis were essentially identical to those obt ained by gas chromatographic and gravimetric analysis of the polymers. X-Ray diffraction analysis of the polymer in the freeze-dried, whole cells and of the isolated, fully crystallized polymer showed that the two types of PHO samples had similar crystal structures, but the polym er in the granules exhibited better side-chain packing and higher crys tallinity. (C) 1998 Elsevier Science B.V. All rights reserved.