Streptomyces sp biodegradation activity on properties of polyhydroxyalkanoates

SILVIA MIYAZAKI,; OXANA YASHCHUK,; ÉLIDA B. HERMIDA; FRANCISCO POVOLO,

Pinamar

Congreso; X Congress of the Panamerican Association for Biochemistry and Molecular Biology; 2005

Polyhydroxyalkanoates (PHA) are of great interest since their properties are similar to those of conventional thermoplastics with the advantage of their complete biodegradation.  In the present work we studied the capacity of isolated Streptomyces sp. to degrade PHB-co-HV in mineral salt media (MSM) and measured the physico-chemical properties of the degraded samples. Degradation and changes in the molecular weight were measured by weight lost and intrinsic viscosimetry, respectively. Degraded samples of PHB-co-HV lost 45% of the initial weight after 45 days of incubation in the inoculated MSM with Streptomyces sp. No significative changes in the mean molecular weight were observed. The surface of the degraded samples, analyzed by SEM, shows few big pores at the beginning of degradation. As the activity of the microorganisms increases a great number of pores, 10 times smaller than the ones first observed, appear. Streptomyces sp. degrades the biopolymer randomly on all over the sample. Crystallinity and mechanical behaviour of the degraded samples were measured by X ray diffraction and tensile tests at constant strain rate, respectively. The ultimate tensile strength of degraded samples decreased up to 64% of the control samples after 30 days with no significative changes in the crystallinity. Extracellular protein was measured by the method of Bradford and the activity of PHA-depolymerase was determined by the clear zone method.