Submitted to: Bio Environmental Polymer Society
Publication Type: Abstract Only
Publication Acceptance Date: 4/20/2006
Publication Date: 6/14/2006
Citation: Ashby, R.D., Solaiman, D., Foglia, T.A. 2006. Macro- and microscopic visual evidence for the biodegradation of poly(hydroxyalkanoates) by pseudomonas lemoignei and comamonas p37c. Bio Environmental Polymer Society. p. 87. Interpretive Summary:
Technical Abstract: Poly(hydroxyalkanoates) (PHAs) are biodegradable through the action of extracellular depolymerase enzymes (carboxyesterases EC 22.214.171.124 and EC 126.96.36.199). Two common methods of assessing PHA biodegradability are by mineralization using respirometry according to ASTM standard D5338-98 where the generation of carbon dioxide is measured upon exposure of the PHA to a controlled composting environment, and by various clear zone techniques where PHAs are suspended in solid media and upon inoculation, microorganisms that synthesize extracellular PHA depolymerases hydrolyze the suspended PHAs to water-soluble products resulting in transparent zones around the bacterial growth. In this paper we describe the use of both tube and plate clear zone techniques to ascertain the ability of Pseudomonas lemoignei and Comamonas P37C (known depolymerase producers) to hydrolyze poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB/Hx; NODAX, Procter & Gamble) and medium-chain-length PHA derived from caprylic acid (PHA-CAP). Each PHA polymer was degraded by at least 1 of the bacterial strains. However, P3HB/Hx promoted degradation to a greater extent than the other PHAs. Those PHA polymers that were positive for degradation were solvent cast into thin films and exposed to the degrading organism as a sole source of carbon. Over time, the films were observed by scanning electron microscopy (SEM) and confocal microscopy (CM) to visually observe the degradation process. The results showed that the surface topography of the films had become less uniform, which is indicative of degradation.