Degradation of three kinds of bioplastics and their effects on microbial biomass and microbial diversity in soil environment were analyzed. The degradation rate of bioplastic in soil was closely related to the main components in the bioplastics. Poly (butylene succinate)-starch (PBS-starch) and poly (butylene succinate) (PBS) were degraded by 1% to 7% after 28 days in a soil with an initial bacterial biomass of 1.4 × 10 9 cells/g-soil, however poly lactic acid (PLA) was not degraded in the soil after 28 days. When the powdered-bioplastics were examined for the degradation in the soil, PBS-starch also showed the highest degradability (24.4% degradation after 28 days), and the similar results were obtained in the case of long-term degradation experiment (2 years). To investigate the effect of bacterial biomass in soil on biodegradability of bioplastics, PBS-starch was buried in three kinds of soils differing in bacterial biomass (7.5 × 10 6 , 7.5 × 10 7 , and 7.5 × 10 8 cells/gsoil). The rate of bioplastic degradation was enhanced accompanied with an increase of the bacterial biomass in soil. 16S rDNA PCR-DGGE analysis indicated that the bacterial diversity in the soil was not affected by the degradation of bioplastics. Moreover, the degradation of bioplastic did not affect the nitrogen circulation activity in the soil.

Aims:  To degrade ether‐type polyurethane (ether‐PUR), ether‐PUR–degrading micro‐organism was isolated. Moreover, ether‐PUR–degrading mechanisms were analysed using model compounds of ether‐PUR. Methods and Results:  A fungus designated as strain PURDK2, capable of changing the configuration of ether‐PUR, has been isolated. This isolated fungus was identified as Alternaria sp. Using a scanning electron microscope, the grid structure of ether‐PUR was shown to be melted and disrupted by the fungus. The degradation of ether‐PUR by the fungus was analysed, and the ether‐PUR was degraded by the fungus by about 27·5%. To analyse the urethane‐bond degradation by the fungus, a degraded product of ethylphenylcarbamate was analysed using GC/MS. Aniline and ethanol were detected by degradation with the supernatant, indicating that the fungus secreted urethane‐bond–degrading enzyme(s). PURDK2 also degraded urea bonds when diphenylmethane‐4,4′‐dibutylurea was used as a substrate. Conclusions:  The enzyme(s) from PURDK2 degraded urethane and urea bonds to convert the high molecular weight structure of ether‐PUR to small molecules; and then the fungus seems to use the small molecules as an energy source. Significance and Impact of the Study:  Ether‐PUR–degrading fungus, strain PURDK2, was isolated, and the urethane‐ and urea‐bonds–degrading enzymes from strain PURDK2 could contribute to the material recycling of ether‐PUR.

Thirty-six bacteria that degraded long-chain hydrocarbons were isolated from natural environments using long-chain hydrocarbons (waste car engine oil, base oil or the c-alkane fraction of base oil) as the sole carbon and energy source. A phylogenetic tree of the isolates constructed using their 16S rDNA sequences revealed that the isolates were divided into six genera plus one family (Acinetobacter, Rhodococcus, Gordonia, Pseudomonas, Ralstonia, Bacillus and Alcaligenaceae, respectively). Furthermore, most of the isolates (27 of 36) were classified into the genera Acinetobacter, Rhodococcus or Gordonia. The hydrocarbon-degradation similarity in each strain was confirmed by the 2,6-dichlorophenol indophenol (2,6-DCPIP) assay. Isolates belonging to the genus Acinetobacter degraded long-chain normal alkanes (n-alkanes) but did not degrade short-chain n-alkanes or cyclic alkanes (c-alkanes), while isolates belonging to the genera Rhodococcus and Gordonia degraded both long-chain n-alkanes and c-alkanes.

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The degradation pathways for cyclic alkanes (c-alkanes) in Rhodococcus sp. NDKK48 were investigated. Strain NDKK48 used dodecylcyclohexane as a sole carbon and energy source, and five metabolites in the dodecylcyclohexane degradation pathway were detected by gas-chromatography/mass spectra. The metabolites were identified as cyclohexanecarboxylic acid, cyclohexylacetic acid, 1-cyclohexene-1-acetic acid, 4-dodecylcyclohexanol, and 4-dodecylcyclohexanone. The strain degrades dodecylcyclohexane via a ring oxidation pathway and an alkyl side chain oxidation pathway. Cyclohexanecarboxylic acid was further oxidized to muconic acid via 1-cyclohexene-1-carboxylic acid and benzoic acid, and the muconic acid was finally used by strain NDKK48 for growth. Methylcyclohexane and cyclohexane were co-oxidized with hexadecane by strain NDKK48. Methylcyclohexane was degraded via a ring oxidation pathway, and the degradation pathway contained part of the Baeyer-Villiger oxidation for ring cleavage. Cyclohexane was also degraded by the same pathway as methylcyclohexane. Thus, strain NDKK48 has two pathways for the complete degradation of c-alkanes.