Immobilization of Aspergillus niger sp. in sol gel and its potential for production of xylanases

Sol gel technique, using tetrametoxysilane (TMOS) as precursor, was evaluated as a method for immobilization of a xylanase-producing Aspergillus niger sp strain. Although alcohol released by the hydrolysis–condensation reaction of silicon alkoxides during sol gel formation usually has a potential denaturing activity for the entrapped biological material, Aspergillus niger cells were resistant to this condition, maintaining part of its microbial activity and xylanase production ability after the immobilization process. Optical microscopy showed a significant mycelia growth in the inner part of the support after incubation in liquid cultures; meanwhile, in shake flasks cultures, immobilized cells maintained 56% of glucose uptake and retained 24% of xylanase activity, compared to free cells after 168 h of incubation at 37 °C. Results suggested that even though this fungus was able to overcome solvent toxicity caused by the sol gel immobilization technique, diffusional limitations were the reason for low glucose consumption and the drop in the production of the enzymatic activity observed. In our knowledge, this study is the first in which the immobilization of an A. niger strain in sol gel material is reported, and from this work further study is underway to improve the characteristics of the gel material used for immobilization, as well as to increase the xylanase and other polysaccharase production by sol gel entrapped fungus.