Heterologous Expression of a Thermostable alpha-Galactosidase from Parageobacillus thermoglucosidasius Isolated from the Lignocellulolytic Microbial Consortium TMC7

alpha-Galactosidase is a debranching enzyme widely used in the food, feed, paper, and pharmaceuticals industries and plays an important role in hemicellulose degradation. Here, T26, an aerobic bacterial strain with thermostable alpha-galactosidase activity, was isolated from laboratory-preserved lignocellulolytic microbial consortium TMC7, and identified as Parageobacillus thermoglucosidasius. The alpha-galactosidase, called T26GAL and derived from the T26 culture supernatant, exhibited a maximum enzyme activity of 0.4976 IU/ml when cultured at 60 degrees C and 180 rpm for 2 days. Bioinformatics analysis revealed that the alpha-galactosidase T26GAL belongs to the GH36 family. Subsequently, the pET-26 vector was used for the heterologous expression of the T26 alpha-galactosidase gene in Escherichia coli BL21 (DE3). The optimum pH for alpha-galactosidase T26GAL was determined to be 8.0, while the optimum temperature was 60 degrees C. In addition, T26GAL demonstrated a remarkable thermostability with more than 93% enzyme activity, even at a high temperature of 90 degrees C. Furthermore, Ca2+ and Mg2+ promoted the activity of T26GAL while Zn2+ and Cu2+ inhibited it. The substrate specificity studies revealed that T26GAL efficiently degraded raffinose, stachyose, and guar gum, but not locust bean gum. This study thus facilitated the discovery of an effective heatresistant a-galactosidase with potent industrial application. Meanwhile, as part of our research on lignocellulose degradation by a microbial consortium, the present work provides an important basis for encouraging further investigation into this enzyme complex.