Investigation of biodegradibilities of some polyhydroxyalkanoates by Pseudomonas isolates

SUMMARY Investigation of biodegradibilities of some polyhydroxyalkanoates by Pseudomonas isolates In this study, polyhydroxyalkanoate biodegradation capabilities of some species isolated from soil and identified previously as Pseudomonas sp. in terms of some physiological and biochemical properties were investigated. Surface morphologies of solution-cast PHB films at the end of 24 h of incubation with the isolates were monitored by Scanning Electron Microscopy. Several irregular pits and erosion on film surfaces exposured to Pseudomonas isolates were observed. Both decrease in molecular weight determined by GPC and weight loss up to 30% have shown that the isolates are able to degrade the films. Degradation of polyhydroxyoctanoate, polyhydroxynonanoate or copolymer (PHB-co-HV) films poured on a solid medium was also observed by clear zone formation after incubation of isolates. The presence of some peptides with molecular weight of 50-60 kDa was electrophoreticly identified. This result is consistent with the earlier observations that a depolymerase with similar molecular weight is present in other Pseudomonas species. Characterization of depolymerase activity was assayed in the presence of /Miitrophenylbutyrate as a substrate and some kinetic data were compared with the reported values. From the data, Km and Vmax values in the presence of the substrate were calculated as 2.3 mM and 2.8 Units, respectively, for the enzyme responsible for this activity. It was also observed that depolymerase activities were stimulated by Na"\ K~ or Mg+2 at specific concentrations but decreased at their greater concentrations. On the contrary, the activation of enzyme in the presence of Ca"2 stay constant even in the presence its higher concentrations. The inhibition behaviour of some chemicals such as phenylmethylsulfonylfluoride, dithiothreitol, cyanide, sodium azide, deoxycholic acid sodium salt and ethylenediamine tetraacetic acid sodium salt on the observed depolymerase activity has evidenced the presence of an enzyme in the isolates similar to depolymerase reported earlier. Moreover, the isolates with PHA degradation properties were identified as Pseudomonas sp. from the 16S rRNA gene analyses. Key words: Polyhydroxybutyrate, Depolymerase, Biodegradability, Pseudomonas VII