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| Author(s): |
Tony Márcio da Silva
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Ribeirão Preto. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC) |
| Defense date: | 2009-11-19 |
| Examining board members: |
Maria de Lourdes Teixeira de Moraes Polizeli;
Hamilton Cabral;
Benevides Costa Pessela João;
Joao Atilio Jorge;
Simone Aparecida Antoniazi Pereira
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| Advisor: | Maria de Lourdes Teixeira de Moraes Polizeli |
| Abstract | |
This study aimed to collect and isolate filamentous fungi from different regions of São Paulo state with potential for amylases production with desirable physical and chemical characteristics for industrial application. It was collected 19 fungi during three different expeditions. These fungi with other five microorganisms previously isolated during the Biota project were submitted to screening tests to select a good amylases producer. Aspergillus niveus was one of the best amylase producers under experimental conditions and was chosen to continue this work. The next step was to determine the best growth conditions for the amylases production. The highest levels of enzymatic synthesis were detected in Khanna medium under static conditions, initial pH 6.0, at 40°C during 72 hours. Corn, oatmeal, rice straw, corn starch, soluble starch, cassava peel, maltose, wheat bran, penetrose, amylopectin and raffinose were the best carbon sources for amylase production. Enzymatic extracts from A. niveus obtained under the optimal culture conditions, were loaded in different chromatography columns (DEAE-Fragtogel and Sephacryl S200) where three amylases were purified (a glucoamylase and two a-glucosidases, named I and II), whose molecular weights determined by SDS-PAGE corresponded to 77, 59 and 55 kDa. The isoelectric points and carbohydrate content were 3.8 and 15% for glucoamylase, 6.6 and 4% for -glucosidase I and 6.8 and 29% for -glucosidase II, respectively. The glucoamylase optimum pH was 5.0-5.5 and 6.0 for -glucosidases I and II. The optimum reaction temperatures were 65° C for all studied enzymes and all of them showed stability at 60 and 65°C. The glucoamylase presented high affinity for starch and -glucosidase I presented high affinity for starch, glycogen and maltose. The highest catalytic efficiency was observed using glycogen, starch and maltose as substrates. The -glucosidase II hydrolyzed several substrates and the kcat/Km values showed greater performance under glycogen, followed by starch, amylopectin, maltose and -NPG hydrolysis. The Circular Dichroism (CD) analyses showed that all the studied amylases were predominantly constituted by -helices in its secondary structure. The amino acid sequencing revealed similarity among the glucoamylase from A. niveus, A. terreus, A. niger, A. ficcum, A. awamori, A. kawachi and A. shirousami. Comparing the sequencing of a-glucosidases I and II from A. niveus, both showed homology with other a-glucosidases from A. fumigatus. Studies about the effect of N-glycans under enzymatic properties were done by addition of tunicamycin in the culture medium. Glucoamylase and a-glucosidase I lost significantly their substrate specificity, and a- glucosidase II lost its thermostability after the N-glycans removal. Glucoamylase and a- glucosidase II were immobilized in ionic interaction supporters and by covalent bonds. The ion exchangers supporters used were glyoxylic-PEI, glyoxylic-MANA, DEAESephacel and Sepharose Q. The supporters used for covalent interaction were agarose activated with cyanogen bromide (BRCN) and glyoxylic-Agarose, pH 10.5. The stability presented with derivatives formed by covalent bonds was higher than those reported for the derivatives formed from ionic bonds. The use of trehalose as an additive really improved the stability of all derivatives. (AU) | |
| FAPESP's process: | 05/54133-5 - Bioprospection in filamentous fungi: study of alpha-amylase and glucoamylase in fungi isolated from the soil, decomposing matter and thermal waters |
| Grantee: | Tony Márcio da Silva |
| Support Opportunities: | Scholarships in Brazil - Doctorate |