One alkalophilic Bacillus sp. strain C-125 (FERM No. 7344) was isolated from soil. From this organism, two types of xylanases, designated xylanase A and xylanase N, were purified by an ammonium sulfate precipitation followed by Biogel P-30 gel filtration, DEAE-cellulose chromatography, and Sephadex G-75 gel filtration. The molecular weights of xylanase A and N were estimated as 43 000 and 16 000, respectively. Immunological experiments indicated that xylanase A and xylanase N were entirely different protein molecules. Xylanase N was most active at pH 6.0–7.0, but xylanase A had a very broad pH activity curve (pH 6–10) and was still active even at pH 12.0. The maximum hydrolysis of xylan by the enzymes was about 25%. Both enzymes split xylan and yielded xylobiose and higher oligosaccharides but could hydrolyze neither xylobiose nor xylotriose. Trans xylosidation activities were detected in both enzymes.

Plastics are beneficial because of their facility, lightness, ease in processing, transparency, and low cost. Although some plastics are reused and recycled, the disposal of a large quantity of used plastic waste poses a great problem. Spacious land is required for burying waste material, and poisonous gas is often emitted when plastic waste is incinerated. Furthermore, abiotic plastics spoil the scenery and the ecological systems of many forms of life. Considering these problems, biodegradable plastics have been the subject of many research papers. Several kinds have been produced, such as poly (b-hydroxybutyrate), polycaprolactone, and polyglycolic acid, and depolymerases capable of degrading these materials have been reported (Benedict et al., 1983;Chu, 1981;Kemnitzer et al., 1992;Reeve et al., 1994;Tanino et al., 1982). Poly-(L-lactide) (PLA), one of these biodegradable plastics, however, is expected to be used widely since its cost has decreased recently; already it is used in the medical field (Leenslag et al., 1987;Penning et al., 1993). PLA and other lactic acid-containing polymers are synthesized chemically (Dubois et al., 1991;Kricheldorf et al., 1992;Penning et al., 1993). Apart from its biodegradability, PLA has attracted attention as a material that can be made from renewable resources such as starch because lactic acid is produced through the fermentation of starch or glucose. It is completely harmless compared with abiotic polymers when used in vessels for edible products. PLA is known to degrade slowly in natural soil, but it takes a long time for degradation to start. It can be hydrolyzed enzymatically (Ebeling et al., 1974;Fukuzaki et al., 1989;Reeve et al., 1994). Nevertheless, only a few reports have been made so far on the direct degradation of PLA by microorganisms.One report concerns a mold capable of assimilating soluble PLA-oligomer and PLA-copolymer with glycerol (Torres et al., 1996). Furthermore, Pranamuda et al. (1997) reported the degradation of PLA by Amycolatopsis sp.In the present study, we isolated a microorganism capable of efficiently degrading homo-PLA film in liquid culture. This strain differs from the one reported by Pranamuda et al. (1997), especially in terms of growth temperature and spore formation. In this report, we describe the identification of the PLA-degrading organism, the PLA-degradation conditions, and the products found in the culture supernatant. Materials and Methods Medium Isolation of a microorganism capable of degrading poly-(L-lactide)Yoko Ikura* and Toshiaki KudoInstitute of Physical and Chemical Research ( RIKEN ), Wako 351-0198, Japan (Received February 1, 1999; Accepted October 19, 1999) The isolation of poly-(L-lactide) (PLA)-degrading microorganisms was investigated. A PLA-degrading actinomycete, strain No. 3118, was isolated and tentatively identified as a member of the genus Amycolatopsis. The optimum conditions for degradation of PLA were 43°C at about pH 7 in a mineral salt medium with a low concentration of organic nutrients (0.002% yea...

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