High Galacto-Oligosaccharide Production and a Structural Model for Transgalactosylation of β-Galactosidase II from Bacillus circulans

Biochemical characterization of a novel C-terminally truncated β-galactosidase from Paenibacillus antarcticus with high transglycosylation activity

The transgalactosylase activity of β-galactosidases offers a convenient and promising strategy for conversion of lactose into high-value oligosaccharides, such as galacto-oligosaccharides (GOS) and human milk oligosaccharides (HMOs). In this study, we cloned and biochemically characterized a novel C-terminally truncated β-galactosidase (PaBgal2A-D) from Paenibacillus antarcticus with high transglycosylation activity. PaBgal2A-D is a member of glycoside hydrolase (GH) family 2. The optimal pH and temperature of PaBgal2A-D were determined to be pH 6.5 and 50°C, respectively. It was relatively stable within pH 5.0-8.0 and up to 50°C. PaBgal2A-D showed high transglycosylation activity for GOS synthesis, and the maximum yield of 50.8% (wt/wt) was obtained in 2 h. Moreover, PaBgal2A-D could synthesize lacto-N-neotetraose (LNnT) using lactose and lacto-N-triose II (LNT2), with a conversion rate of 16.4%. This study demonstrated that PaBgal2A-D could be a promising tool to prepare GOS and LNnT.

Synergistic enzymatic mechanism of lepidolite leaching enhanced by a mixture of Bacillus mucilaginosus and Bacillus circulans

Numerous studies have demonstrated that the co-leaching of ores by different silicate bacteria significantly improves the performance of bioleaching systems. Nevertheless, the mechanism of different silicate bacteria synergistically or complementarily enhanced the leaching process of lithium-containing silicate remains unclear. This study discussed the leaching impact of the combined presence of two metabolically distinct silicate bacteria on lepidolite, with the aim of comprehending the synergistic effect resulting from the presence of Bacillus mucilaginosus and Bacillus circulans in the leaching process. The results indicated that the polysaccharides and proteins secreted by bacteria-containing functional groups such as -OH and -COOH, which played an important role in the complex decomposition of ores. Organic acids played the role of acid etching and complexation. Bacillus mucilaginosus and Bacillus circulans exhibited low individual leaching efficiency, primarily due to their weak organic acid secretion. Moreover, the prolific polysaccharide production by Bacillus mucilaginosus led to bacterial aggregation, diminishing contact capability with minerals. Bacillus circulans decomposed the excessive polysaccharides produced by Bacillus mucilaginosus through enzymatic hydrolysis in the co-bioleaching process, providing later nutrient supply for both strains. The symbiosis of the two strains enhanced the synthesis and metabolic capabilities of both strains, resulting in increased organic acid secretion. In addition, protein and humic acid production by Bacillus mucilaginosus intensified, collectively enhancing the leaching efficiency. These findings suggested that the primary metabolic products secreted by different bacterial strains in the leaching process differ. The improvement in bioleaching efficiency during co-leaching was attributed to their effective synergistic metabolism. This work contributes to the construction of an efficient engineering microbial community to improve the efficiency of silicate mineral leaching, and reveals the feasibility of microbial co-culture to improve bioleaching.

Sensory Assessment of Bi-Enzymatic-Treated Glucose-Galactose Syrup

There are a variety of ways to make glucose-galactose syrup (GGS) and other products of lactose hydrolysis; therefore, research is still ongoing and will undoubtedly result in improved methods and lower costs. The aim of the study was to use a two-stage fermentation approach to increase the sweetness of glucose-galactose syrup. Comparing lactose hydrolysis with β-galactosidases, the enzyme Ha-Lactase 5200 (K. lactis) showed the highest hydrolysis yield but NOLA™ Fit5500 (B. licheniformis) and GODO-YNL2 (K. lactis) hydrolysis yields varied. After the two-stage fermentation, the syrups from sweet whey permeate had shown the highest sweet taste intensity scores; the sweetest samples were 1NFS and 1HLS with a score of 9.2 and 9.3, respectively. The presence of fructose in the range of 14 ± 3 to 25 ± 1 %, significantly (p < 0.05) increased the sweetness of the syrups. Obtained syrups from whey permeates using enzymes NOLA™ Fit5500 and Ha-Lactase 5200 contained less than 10% lactose. Additionally, results indicate that hydrolysis of lactose and subsequent enhancement of sweetness through glucose isomerisation may provide additional benefits through the production of galacto-oligosaccharides (GOS) in the range of 2 ± 1 to 34 ± 7%.

β-galactosidase GALA from Bacillus circulans with high transgalactosylation activity

β-galactosidase catalyzes lactose hydrolysis and transfers reactions to produce prebiotics such as galacto-oligosaccharides (GOS) with potential applications in the food industry and pharmaceuticals. However, there is still a need for improved transgalactosylation activity of β-galactosidases and reaction conditions of GOS production in order to maximize GOS output and reduce production costs. In this study, a β-galactosidase gene, galA, from Bacillus circulans was expressed in Pichia pastoris, which not only hydrolyzed lactose but also had strong transgalactosylation activity to produce GOS. Response surface methodology was adopted to investigate the effects of temperature, enzyme concentration, pH, initial lactose concentration, and reaction time on the production of GOS and optimize the reaction conditions for GOS. The optimal pH for the enzyme was 6.0 and remained stable under neutral and basic conditions. Meanwhile, GALA showed most activity at 50°C and retained considerable activity at a lower temperature 30–40°C, indicating this enzyme could work under mild conditions. The enzyme concentration and temperature were found to be the critical parameters affecting the transgalactosylation activity. Response surface methodology showed that the optimal enzyme concentration, initial lactose concentration, temperature, pH, and reaction time were 3.03 U/mL, 500 g/L, 30°C, 5.08, and 4 h, respectively. Under such conditions, the maximum yield of GOS was 252.8 g/L, accounting for approximately 50.56% of the total sugar. This yield can be considered relatively high compared to those obtained from other sources of β-galactosidases, implying a great potential for GALA in the industrial production and application of GOS.