Biodegradation of polyvinyl alcohol using cross-linked enzyme aggregates of degrading enzymes from Bacillus niacini.

In this study, polyvinyl alcohol (PVA)-degrading bacteria were screened from sludge samples using PVA as a sole source of carbon. A novel strain was obtained and identified as Bacillus niacini based on the analysis of a partial 16S rDNA nucleotide sequence and morphological characteristics. PVA-degrading enzyme (PVAase) from Bacillus niacini was immobilized as cross-linked enzyme aggregates (CLEAs) via precipitation with ammonium sulfate followed by glutaraldehyde cross-linking. The effects of precipitation and cross-linking on PVAase-CLEAs activity were investigated and characterized. 70% ammonium sulfate and 1.5% glutaraldehyde were used for precipitation and 1-h cross-linking reaction. The activity recovery of PVAase-CLEAs was approximately 90% starting from free PVAase, suggesting non-purification steps are required for extended use. No significant differences in optimum pH and temperature values of the PVAase were recorded after immobilization. The PVAase-CLEAs showed a ball-like morphology and enhanced PVA degradation efficiency in comparison with the free PVAase in solution. Furthermore, the PVAase-CLEAs exhibited excellent thermal stability, pH stability and storage stability compared to free PVAase. The PVAase-CLEAs retained about 75% of initial PVAase activity after 4 cycles of use. These results suggest that this CLEA is potentially usable for PVA degradation in industrial applications.

Bienzyme Magnetic Nanobiocatalyst with Fe3+-Tannic Acid Film for One-Pot Starch Hydrolysis.

In this study, a novel co-immobilization biocatalyst for one-pot starch hydrolysis was prepared through shielding enzymes on the Fe3O4/SiO2 core-shell nanospheres by a Fe3+-tannic acid (TA) film. In brief, α-amylase and glucoamylase were covalently immobilized on amino-modified Fe3O4/SiO2 core-shell nanospheres using glutarldehyde as a linker. Then, a Fe3+-TA protective film was formed through the self-assembly of the Fe3+ and TA coordination complex (Fe3+-TA@Fe3O4/SiO2-enzymes). The film acts a "coating" to prevent the enzyme from denaturation and detachment, thus significantly improving its structural and operational stability. Furthermore, the immobilization efficiency reached 90%, and the maximum activity recovery of α-amylase and glucoamylase was 87 and 85%, respectively. More importantly, the bienzyme magnetic nanobiocatalyst with Fe3+-TA film could be simply recovered by a magnet. The Fe3+-TA@Fe3O4/SiO2-enzymes kept 55% of the original activity after reuse for 9 cycles, indicating outstanding reusability. However, the bienzyme magnetic nanobiocatalyst without Fe3+-TA film maintained 28% of the initial activity.