Sol-gel nanomaterials with algal heteropolysaccharide for immobilization of microbial cells, producing a-galactosidase and nitrilase

Abstract

The main purpose of the present work is the sol-gel synthesis and structure of the hybrid nanomaterials as matrices for two types of cells, producing hydrolytic enzymes. The effect of different percent of algal polysaccharide included in them on the hydrolytic activity of fungal and bacterial cells was investigated. The hybrid sol-gel nanomaterials were synthesized from tetraethylortosilicate (TEOS) as a silicon precursor and heteropolysaccharide (AHPS) from the red microalga Dixonella grisea as an organic part. The structure of these matrices was investigated using different methods: FT-IR, XRD, BET-Analysis, EDS, SEM and AFM. The sol-gel hybrids were used for the immobilization of fungal (Humicola lutea) and bacterial (Bacillus sp.) cells, producing α-galactosidase and nitrilase, respectively. It was established the effect of the quantity of the heteropolysaccharide in the matrices on the activity of these hydrolytic enzymes. Using 20% AHPS in the hybrid nanomaterials the α-galactosidase yield exceeded over two-fold the enzyme titre of the free cells in the third cycle of repeated batch shake flask cultivation. These results correlated with a dense growth of immobilized mycelium observed with scanning electron microscopy (SEM). The increase of the percentage of organic part in the sol-gel matrix up to 20% led to an increase in the nitrilase activity. The addition of 40% AHPS did not significantly affect the decrease of the nitrile biodegradation. © 2009 Taylor and Francis Group, LLC.