Improvement in the Thermostability of a Recombinant β-Glucosidase Immobilized in Zeolite under Different Conditions

Stability Enhancement of Aldehyde Dehydrogenase from Anoxybacillus geothermalis Strain D9 Immobilized onto Seplite LX120

Enzyme stability is regarded as an important criterion for an industrial biocatalyst. Aldehyde dehydrogenase (ALDH) from A. geothermalis strain D9 was previously reported to exhibit good thermostability. However, this enzyme is still not suited to use in harsh environments. In this current work, we aim to see the viability of ALDH in terms of stability when immobilized into Seplite LX120. The purified ALDH was successfully immobilized via physical adsorption at 4 h with 1.25 mg/mL enzyme loading. The immobilized ALDH exhibited improved stability compared to free ALDH as the optimum temperature increased up to 80 °C and was stable with temperatures ranging from 30 to 90 °C. It was also stable in broad pH, ranging from pH 4 to pH 12. Moreover, more than 50% of the immobilized ALDH activity was retained after being stored at 25 °C and 4 °C for 9 and 11 weeks, respectively. The reusability of immobilized ALDH is up to seven cycles. The corroboration of ALDH immobilized on the Seplite LX120 was verified via Fourier-transform infrared spectroscopy, scanning electron microscopy, and a reduction in the surface area. The improved features of immobilized ALDH, especially in enzyme stability, are important for future applications.

Enhancing the ethanol production by exploiting a novel metagenomic-derived bifunctional xylanase/β-glucosidase enzyme with improved β-glucosidase activity by a nanocellulose carrier

Some enzymes can catalyze more than one chemical conversion for which they are physiologically specialized. This secondary function, which is called underground, promiscuous, metabolism, or cross activity, is recognized as a valuable feature and has received much attention for developing new catalytic functions in industrial applications. In this study, a novel bifunctional xylanase/β-glucosidase metagenomic-derived enzyme, PersiBGLXyn1, with underground β-glucosidase activity was mined by in-silico screening. Then, the corresponding gene was cloned, expressed and purified. The PersiBGLXyn1 improved the degradation efficiency of organic solvent pretreated coffee residue waste (CRW), and subsequently the production of bioethanol during a separate enzymatic hydrolysis and fermentation (SHF) process. After characterization, the enzyme was immobilized on a nanocellulose (NC) carrier generated from sugar beet pulp (SBP), which remarkably improved the underground activity of the enzyme up to four-fold at 80°C and up to two-fold at pH 4.0 compared to the free one. The immobilized PersiBGLXyn1 demonstrated 12 to 13-fold rise in half-life at 70 and 80°C for its underground activity. The amount of reducing sugar produced from enzymatic saccharification of the CRW was also enhanced from 12.97 g/l to 19.69 g/l by immobilization of the enzyme. Bioethanol production was 29.31 g/l for free enzyme after 72 h fermentation, while the immobilized PersiBGLXyn1 showed 51.47 g/l production titre. Overall, this study presented a cost-effective in-silico metagenomic approach to identify novel bifunctional xylanase/β-glucosidase enzyme with underground β-glucosidase activity. It also demonstrated the improved efficacy of the underground activities of the bifunctional enzyme as a promising alternative for fermentable sugars production and subsequent value-added products.