Biodegradation of poly(3-hydroxyalkanoic acids) fibers and isolation of poly(3-hydroxybutyric acid)-degrading microorganisms under aquatic environments

Abstract

Biodegradabilities of poly[(R)-3-hydroxybutyric acid- co-14mol%(R)-3-hydroxyvaleric acid] (P(3HB- co-14%3HV)) monofilament fibers were evaluated at 25°C for 28 days by monitoring the time-dependent changes in the biochemical oxygen demand (BOD) and weight-loss (erosion) of fibers under aerobic conditions in a temperature-controlled reactor containing natural waters from various aquatic environments (seawater, lake freshwater and river freshwater in Japan). Two types of fibers with different diameters (213 and 493 μm) were used in this test. The biodegradabilities of fibers decreased in the following order: river freshwater > lake freshwater > seawater. By analyses of scanning electron microscopy and X-ray diffraction of eroded fibers, it has been concluded that the biodegradation proceeded from amorphous regions on the surface of fibers by the function of microorganisms in freshwater or seawater. In addition, 13 strains of P(3HB)-degrading bacteria were isolated from different sources of seawater and identified. Majority of isolates grew well on P(3HB) or P(3HB- co-14%3HV) as sole carbon source and excreted extracellular polyhydroxybutyrate (PHB) depolymerases.