Investigations on the biodegradation of polyesters by isolated mesophilic microbes

Abstract

The biodegradation of synthetic polyesters such as poly(tetramethylene adipate – co – tetramethylene terephthalate) (BTA), poly(e-caprolactone) (PCL) and polytetramethylene-adipate (SP 4/6) as well as the natural copolyester poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) was investigated under mesophilic conditions. Microorganisms capable of hydrolyzing polyesters were isolated from mature compost and gardening soil. Eight strains from a total of 47 BTA and PCL hydrolyzing isolates could be assigned to the groups of mesophilic fungi (Arthrobotrys amerospora DSM 15963, Acremonium strictum DSM 15965, Cladosporium herbarum DSM 15967, Fusarium solani DSM 15964, Aspergillus fumigatus DSM 15966) and actinomycetes (Microbispora rosea subsp. Rosea DSM 44767 and DSM 44768, Streptomyces thermocarboxydus DSM 41841). Three fungal isolates (A. amerospora, A. strictum, C. herbarum) are specialized on the degradation of the synthetic polyesters, while two fungi (F. solani, A. fumigatus) and three actinomycetes strains (M. rosea subsp. rosea and S. thermocarboxydus) exhibited a wider substrate spectrum as they are able to degrade synthetic as well as natural polyesters. The synthetic and natural aliphatic polyesters were degraded faster than BTA 45:55 by most isolates. However, the strain A. amerospora degraded the aliphatic-aromatic copolyester BTA faster than PCL. Three fungal strains (F. solani, C. herbarum, A. strictum) showed also significant degradation potential for the polymer films at low temperatures (4°C). Extracellular PCL depolymerizing enzymatic activity in the supernatant of a culture from the strain M. rosea subsp. rosea could be identified. Regarding the different polyester structures, the enzyme showed a broad substrate specificity for different synthetic polyesters. However, in contrast to the whole organism, the enzyme was not active against the microbial polyester PHBV.