BIODEGRADATION OF POLY(3-HYDROXYALKANOATES) IN ANAEROBIC SLUDGE AND CHARACTERIZATION OF A POLY(3-HYDROXYALKANOATES) DEGRADING ANAEROBIC BACTERIUM

The degradation of samples of poly(3-hydroxybutyrate) [P(3HB)], copoly mers of 3-hydroxybutyrate and 10 and 20% 3-hydroxyvalerate [P(3HB-co-3 HV)], and poly(3-hydroxyoctanoate-co-3-hydroxydecanoate) [P(3HO-co-3HD )] in anaerobic sludge was investigated by gravimetry, changes in mole cular weight and mechanical properties. After 123 days, the mass of P( 3HB) decreased by 15%. P(3HB-co-3HV) showed 7 and 11% mass loss, while P(3HO-co-3HD) showed no change in mass. The average molecular weight of all samples decreased with incubation rime bur this decrease was no t correlated to the loss of mass, and is to be attributed to abiotic h ydrolysis. The tensile strength of the P(3HB) and P(3HB-co-3HV) sample s decreased with incubation time, but elongation remained practically unchanged. By enumeration, it was shown that anaerobic P(3HB) degradin g bacteria were enriched during the incubation period. An anaerobic ba cterium LMG 16094, able to degrade P(3HB) and P(3HB-co-19% 3HV) in pur e culture, but not P(3HB-co-97% 3HV), P(3HO-co-3HD) or poly(epsilon-ca prolactone), was isolated and characterized by fatty acid analysis. It s cells contained mainly straight chain, saturated and unsaturated fat ty acids, with a high portion of fatty acids with 16 carbons, and did not contain hydroxylated or branched fatty acids. Its 16 rDNA gene seq uence was found to be related to those of members of Clostridium group I (Collins er al., 1994). In a simple in vitro test using strain LMG 16094 in pure culture, an extruded P(3HB-co-12% 3HV) film lost 10% of its initial mass within 21 days of anaerobic incubation.