SCANNING ELECTRON-MICROSCOPY OF POLYHYDROXYALKANOATE DEGRADATION BY BACTERIA

Bacterial degradation of sheets of selected polyhydroxyalkanoates by C omamonas sp., Pseudomonas lemoignei and Pseudomonas fluorescens GK13 i s reported. Five natural polyhydroxyalkanoates were used, namely poly( 3-hydroxybutyrate), poly(3-hydroxyvalerate), a copolymer of 3-hydroxyb utyrate and 3-hydroxyvalerate, a copolymer of mainly 3-hydroxyoctanoat e and minor amounts of 3-hydroxyhexanoate, and two rubber-like copolym ers of saturated and unsaturated hydroxyalkanoic acids that had been m odified by electron-beam-induced cross-linking. Each of these polymers was degraded by at least one bacterial strain, the rate of hydrolysis being dependent on the surface area of the polymer exposed to attack. Scanning electron microscopy of partially degraded samples showed tha t hydrolysis started at the surface and at physical lesions in the pol ymer and proceeded to the inner part of the material. No evidence for areas of non-degradable polymer was round for any of the polymers anal ysed, even if the polymer contained chemical cross-links.