Cellulases de souches fongiques issues du sol d'un milieu extreme (sol proche de sources thermales)

Abstract

Filamentous fungi found in soils surrounding the hydrothermal stations of regions in the east of Algeria: Guelma (Hammam Debagh) and Mila (Hammam Grouz-Atmania, Hammam Safsaf-Teleghma), are screened for the presence of cellulase activity. 88 fungal strains were isolated and identified as belonging to six genera: Aspergillus, Alternaria, Emericella, Fusarium, Penicillium and Trichoderma. Their selection (filter paper test and test of perforated plates) shows that only the strain J2 has a significant cellulolytic activity. This isolate belongs to the species of Trichoderma longibrachiatum Rifai. At 35°C, our isolate shows equivalent activities filter paper and endoglucanase than T. reesei. On the other hand the β-glucosidase activity of our isolate was until twice more important than T. reseei one. With an inoculum size of 106 spores/ml the strain produces the maximum enzyme activities. A good yield of enzyme is obtained with spores aged of six days. The strain D allowed from subcloning cultivated in 4 liters fermenter on Mandels medium with cellulose Avicel (1%) produces maximum activities of filter paper (1.88UI/ml), endoglucanase (11.22UI/ml) and β- glucosidase (0.66UI/ml) after 128 hours, 144 hours and 120 hours, respectively. The optimum temperatures were 55°C and 60°C for endoglucanase and FPA, respectively. The endoglucanase was optimally active at pH 4.0, and the FPA was optimal at pH 4.0 and 5.0. The endoglucanase was thermostable at 70°C after 5 hours incubation, preserved 80% of the original activity. The half-life of the filter paper activity appeared to be 3 hours at 60°C. These activities were stable at 50°C after 5 hours incubation in a pH range of 3.0 to 6.0 and 4.0 to 6.0, respectively. The EDTA (5mM) causes a significant diminution of the cellulasic activity, while the β-mercaptoethanol (5mM) leading to their activation. Divalent cations calcium (Ca2+) and zinc (Zn2+) cause an increase and improvement of enzymes activities in the presence of EDTA (5mM). The crude enzyme extract is able to hydrolyse insoluble cellulosic substrates. This enzyme can be classified as an endo and exo type of the cellulase. These results suggested that the no-mutated strain Trichoderma longibrachiatum should be an attractive producer for cellulases production.