الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 210 |  |  |
| | | from | 210 | | |
Abstract
Cellulose is a long linear homopolymer consisting of D- glucose units connected by β-1,4-glycosidic linkages. It is the most abundant biopolymer produced on Earth as a renewable bioresource. Cellulose fibers have a wide range of different technological applications. Also the different conversion of cellulosic fibers into nanoscale improves their characteristics. There are different methods for conversion of cellulose into nanoparticles such as: mechanical, chemical and biological. Because of the environmental hazard and high energy consumption in the mechanical and chemical methods, there was the need to study, develop and optimize green eco-friendly method for nanocellulose preparation by using microbial cellulase producer.
The obtained results could be summarized at the following points:
1. Fifty microbial isolates (21 Fungi, 4 actinobacteria and 25 bacteria) were obtained from different locations contain cellulosic source in Egypt, purified and screened for their cellulase production using iodine test and dinitrosalicylic acid assay.
2. Out of fifty isolates, twenty- one isolates (10 fungi, 3 actinobacteria and 8 bacteria) had cellulase activity on Czapek-Dox medium supported with microcrystalline cellulose (MCC).
3. Three fungal isolates were chosen out of 21 microbial isolates that quantitative screened for cellulase activity. These isolates were named (16Cc, 1Ca and 20Cb) according to different locations.
4. 16Cc, 1Ca and 20Cb fungal isolates were identified based on their cultural, morphological and molecular studies of 18S rRNA and named as Aspergillus flavus, Penicillium chrysogenum and Aspergillus niger, respectively. These isolates were recorded in the Gene Bank under accession numbers ON428526 for A. flavus, ON428527 for P. chrysogenum and OQ3437221 for A. niger.
5. The nutritional and environmental parameters were optimized for the three fungal isolates Aspergillus flavus (16Cc), Penicillium chrysogenum (1Ca) and Aspergillus niger (20Cb) to obtain the highest cellulase activity
• The best temperature of cellulase activity for the three fungal isolates was 28˚C at pH 6 incubated for 9 days at modified Czapek-Dox broth contained microcrystalline cellulose as a sole carbon source and sodium nitrate as nitrogen source in static condition.
6. The obtained filterate was centrifuged and purified by ultrasonication and stand in a water bath at 100 ˚C for 1 hour then washed three times by ethanol.
7. The produced nanocellulose fibers characterized by
• Fourier-transform infrared spectroscopy (FTIR)
• X-Ray diffraction analysis (XRD)
• Scanning electron microscope (SEM)
• Transmission electron microscopy (TEM)
• Thermal gravimetric analysis (TGA)
• Dynamic light scattering (DLS)
These results affirmed that the three selected fungal isolates produced modified cellulose with a different size (176 nm crystal length and 14.6 nm crystal width). These characterizations clarify the homogeneity of the produced nanocellulose fiber which also had thermal stability at high temperatures. The zeta measurements were confirmed that the sample treated with isolate A. flavus exhibited a good stability with average zeta value -20.5 mV which referred to excellent particle stability in the colloidal solutions.
8. The produced nanocellulose fibers used as a carrier for Methionine gamma lyase (MGL) enzyme and screened for their ability to (MGL) immobilization. The results showed that the percentage of enzyme loading activity on the microcrystalline cellulose and on the produced nanocellulose fiber were 74.83 and 90.53%, respectively.
9. The most potent effect of pH on methionine gamma lyase catalytic activity was 7.7 pH when the enzyme was immobilized on the produced nanocellulose fiber at 40˚C as the most effective temperature.
10. Reusability for the immobilized enzyme was tested for 7 cycles, enzyme catalytic activity was 47.5% at the 7th cycle when immobilized on the produced nanocellulose fiber but when immobilized on microcrystalline cellulose the enzyme catalytic activity was 32.6% at the 5th cycle.
11. Storage stability of the immobilized enzyme was screened at room temperature for ten days; the results showed that immobilization on the produced nanocellulose fiber preserve the catalytic activity at 53.8% after 10 days at room temperature as compared with the free enzyme catalytic activity was at 3.8%.