Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni animali, Sezione di Scienze Agrochimiche, Università di Catania, Via S. Sofia 98, 95123 Catania, Italy.
Environ Sci Pollut Res Int. 2011 Jul;18(6):865-70. doi: 10.1007/s11356-011-0443-2. Epub 2011 Jan 25.
BACKGROUND, AIM, AND SCOPE: The disposal problem due to non-degradable petroleum-based plastics has raised the demand for biodegradable polymers. The degradation of poly (lactic acid) (PLA) has been studied for several years, but the understanding of involved mechanisms is still incomplete. Based on our previous studies, and it is hypothesized an enzymatic involvement, the aim of this study was to continue investigations on the degradation of PLA and its nanocomposites by Bacillus licheniformis.
Biodegradation of PLA and its nanocomposites (CLOISITE 30B and SOMASIF MEE) was performed on compression-molded, 25 × 25 × 0.6-mm films. Firstly, two plastic films were dipped into sterile nutrient broth inoculated with B. licheniformis and incubated at 32°C. Then, to verify if biodegradation was due to extracellular esterase, the culture broth was filtered to remove B. licheniformis cells, and the plastic materials were put into this broth.
PLA degradation by B. licheniformis was accelerated by the presence of organoclays. After 5 months in liquid culture, nanocomposites showed only the 10% of residual mass, compared with the 60% of pure PLA. Extracellular esterase activity was detected in the filtered culture broth confirming that PLA biodegradation was probably due to this enzyme action.
背景、目的和范围：由于不可降解的石油基塑料而产生的处理问题，提高了对可生物降解聚合物的需求。多年来一直在研究聚乳酸（PLA）的降解，但对涉及的机制的理解仍不完整。基于我们之前的研究，并假设存在酶的参与，本研究的目的是继续研究地衣芽孢杆菌对 PLA 及其纳米复合材料的降解作用。
通过压缩成型，制备了 25×25×0.6-mm 薄膜的 PLA 及其纳米复合材料（CLOISITE 30B 和 SOMASIF MEE）。首先，将两片塑料薄膜浸入无菌营养肉汤中，接种地衣芽孢杆菌，并在 32°C 下培养。然后，为了验证生物降解是否是由于细胞外酯酶引起的，将培养液过滤以去除地衣芽孢杆菌细胞，并将塑料材料放入该培养液中。
地衣芽孢杆菌对 PLA 的降解作用被有机粘土所加速。在液体培养 5 个月后，纳米复合材料的残余质量仅为 10%，而纯 PLA 的残余质量为 60%。在过滤后的培养液中检测到细胞外酯酶活性，证实 PLA 的生物降解可能是由于这种酶的作用。
