Microbial degradation of poly-β-hydroxybutyrate using landfill soils

The population of poly-β-hydroxybutyrate-degrading microorganisms and the biodegradation of PHB in local landfill soils were examined in vitro and in vivo. Forty-two PHB-degraders consisting of 12 bacteria, 25 actinomycetes and 5 moulds were isolated. The total PHB-degraders averaged 4.7 × 10⁷ and 20 × 10⁴ colony forming units (cfu)/g for San Mateo wet and dry soils, respectively, and 2.3 × 10⁷ and 8.5 × 10⁴ cfu/g for Carmona wet and dry samples, respectively. The PHB-degraders formed 0–59% of the total microbial population in San Mateo and 8–42% in Carmona. Complete (100%) degradation of PHB powder was observed for Chryseomonas-27 and Aspergillus-39 on day 5 in shake flask culture and for Streptomyces-4 on day 7. Burial test in landfill soils showed a 90–91% weight loss of PHB film strips within four weeks; the weight loss of polypropylene film strips was up to 0.12% only. Scanning electron micrographs of degraded films revealed the attachment of microbial cells and fungal mycelium and spores on the surfaces. Holes and cavities were also noted due to the microbial degradation processes.