Ghanem Nevine B, Mabrouk Mona E S, Sabry Soraya A, El-Badan Dalia E S
Botany Department, Faculty of Science, Alexandria University, Egypt.
J Gen Appl Microbiol. 2005 Jun;51(3):151-8. doi: 10.2323/jgam.51.151.
This is the first report on the degradation of poly(3-hydroxybutyrate) (PHB), and its copolymers poly(3-hydroxyvalerate) P(3HB-co-10-20% HV) by Nocardiopsis aegyptia, a new species isolated from marine seashore sediments. The strain excreted an extracellular PHB depolymerase and grew efficiently on PHB or its copolymers as the sole carbon sources. The degradation activity was detectable by the formation of a transparent clearing zone around the colony on an agar Petri plate after 25 days, or a clearing depth under the colony in test tubes within 3 weeks. The previous techniques proved that the bacterium was able to assimilate the monomeric components of the shorter alkyl groups of the polymers. Nocardiopsis aegyptia hydrolyzed copolymers 10-20% PHBV more rapidly than the homopolymer PHB. The bacterial degradation of the naturally occurring sheets of poly(3-hydroxybutyrate), and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was observed by scanning electron microscopy (SEM). The samples were degraded at the surface and proceeded to the inner part of the materials. Clear morphological alterations of the polymers were noticed, indicating the degradative capability of the bacterium. Plackett-Burman statistical experimental design has been employed to optimize culture conditions for maximal enzyme activity. The main factors that had significant positive effects on PHB depolymerase activity of Nocardiopsis aegyptia were sodium gluconate, volume of medium/flask and age of inoculum. On the other hand, MgSO4.7H2O, KH2PO4, K2HPO4 and NH4NO3 exhibited negative effects. Under optimized culture conditions, the highest activity (0.664 U/mg protein) was achieved in a medium predicted to be near optimum containing (in g/L): PHB, 0.5; C6H11O7Na, 7.5; MgSO4.7H2O, 0.35; K2HPO4, 0.35; NH4NO3, 0.5; KH2PO4, 0.35; malt extract, 0.5 and prepared with 50% seawater. The medium was inoculated with 1% (v/v) spore suspension of 7 days old culture. Complete clarity of the medium was achieved after 3 days at 30 degrees C.
这是关于从海洋海岸沉积物中分离出的新物种埃及诺卡氏菌对聚（3-羟基丁酸酯）（PHB）及其共聚物聚（3-羟基戊酸酯）P（3HB-co-10-20% HV）降解的首次报道。该菌株分泌一种细胞外PHB解聚酶，并能以PHB或其共聚物作为唯一碳源高效生长。25天后，在琼脂平板上菌落周围形成透明的澄清区，或3周内在试管中菌落下方出现澄清深度，即可检测到降解活性。先前的技术证明该细菌能够同化聚合物中较短烷基的单体成分。埃及诺卡氏菌水解10-20% PHBV共聚物的速度比均聚物PHB更快。通过扫描电子显微镜（SEM）观察了天然存在的聚（3-羟基丁酸酯）片材及其共聚物聚（3-羟基丁酸酯-co-3-羟基戊酸酯）的细菌降解情况。样品在表面开始降解并向材料内部推进。观察到聚合物有明显的形态变化，表明该细菌具有降解能力。采用Plackett-Burman统计实验设计来优化培养条件以获得最大酶活性。对埃及诺卡氏菌PHB解聚酶活性有显著正向影响的主要因素是葡萄糖酸钠、培养基/烧瓶体积和接种物菌龄。另一方面，MgSO4·7H2O、KH2PO4、K2HPO4和NH4NO3表现出负面影响。在优化的培养条件下，在预计接近最佳的培养基中（每升含：PHB, 0.5；C6H11O7Na, 7.5；MgSO4·7H2O, 0.35；K2HPO4, 0.35；NH4NO3, 0.5；KH2PO4, 0.35；麦芽提取物, 0.5，并由50%海水配制）获得了最高活性（0.664 U/mg蛋白）。用7日龄培养物的1%（v/v）孢子悬浮液接种该培养基。在30℃下3天后培养基完全澄清。
