Date Published: August 2, 2012
Author(s): Motoo Koitabashi, Masako T Noguchi, Yuka Sameshima-Yamashita, Syuntaro Hiradate, Ken Suzuki, Shigenobu Yoshida, Takashi Watanabe, Yukiko Shinozaki, Seiya Tsushima, Hiroko K Kitamoto.
To improve the biodegradation of biodegradable plastic (BP) mulch films, 1227 fungal strains were isolated from plant surface (phylloplane) and evaluated for BP-degrading ability. Among them, B47-9 a strain isolated from the leaf surface of barley showed the strongest ability to degrade poly-(butylene succinate-co-butylene adipate) (PBSA) and poly-(butylene succinate) (PBS) films. The strain grew on the surface of soil-mounted BP films, produced breaks along the direction of hyphal growth indicated that it secreted a BP-degrading enzyme, and has directly contributing to accelerating the degradation of film. Treatment with the culture filtrate decomposed 91.2 wt%, 23.7 wt%, and 14.6 wt% of PBSA, PBS, and commercially available BP polymer blended mulch film, respectively, on unsterlized soil within 6 days. The PCR-DGGE analysis of the transition of soil microbial community during film degradation revealed that the process was accompanied with drastic changes in the population of soil fungi and Acantamoeba spp., as well as the growth of inoculated strain B47-9. It has a potential for application in the development of an effective method for accelerating degradation of used plastics under actual field conditions.
Agricultural mulch films, which are used for covering cultivated fields to maintain a stable soil temperature and to prevent weeds from growing, are the most common and highly consumed plastic products on agricultural farm lands. The widespread use of mulch films however, has led to an increase in environmental wastes particularly because the removal and disposal of used mulch films is highly cumbersome and consumes a lot of energy (Kyrikou and Briassoulis ).
In the present study, we determined the potential of using BP degrading- microorganisms for accelerating the degradation of used BP mulch films in agricultural fields. Several studies concerning fungi that possess the ability to degrade plastics have already been reported. A Fusarium solani f. sp. pisi, a plant pathogenic fungus degraded BP of poly (ϵ-caprolactone) (PCL) emulsion (Murphy et al. ). Heterologously expressed cutinases of plant pathogenic fungi (F. solani f. sp. pisi, Alternaria brassicicolaAspergillus fumigates and Humicola insolens) degraded PCL film (Baker et al. ). Aspergillus oryzae, a fungus widely used in traditional Japanese fermentation industries, degraded PBS and PBSA mulch film (Maeda et al. ). To address safety concerns regarding the use of microorganisms in the agricultural fields, in this study, we performed our microbial isolation from gramineous crop plants. Our results showed that 4.5% of the isolated fungal strains degraded PBSA emulsion. We have previously reported in a related study that 2% to 100% of yeast populations isolated from seed rice husks degraded PBSA emulsion (Kitamoto et al. ). These findings thus demonstrate that phylloplane is an important source of BP-degrading eukaryotic microorganisms. Further analysis and identification of the evaluated fungal strains could be expected to give us detailed information about the diversity and activities of BP-degrading phylloplane-derived fungi.
The authors declare that they have no competing interests.