Challenges and perspectives of the β-galactosidase enzyme

Biochemical characterization of a novel β-galactosidase from Pedobacter sp. with strong transglycosylation activity at low lactose concentration

A novel β-galactosidase gene (PbBgal35A) from Pedobacter sp. CAUYN2 was cloned and expressed in Escherichia coli. The gene had an open reading frame of 1917 bp, encoding 638 amino acids with a predicted molecular mass of 62.3 kDa. The deduced amino acid sequence of the gene shared the highest identity of 41% with a glycoside hydrolase family 35 β-galactosidase from Xanthomonas campestris pv. campestris (AAP86763.1). The recombinant β-galactosidase (PbBgal35A) was purified to homogeneity with a specific activity of 65.9 U/mg. PbBgal35A was optimally active at pH 5.0 and 50 °C, respectively, and it was stable within pH 4.5‒7.0 and up to 45 °C. PbBgal35A efficiently synthesized galacto-oligosaccharides from lactose with a conversion ratio of 32% (w/w) and fructosyl-galacto-oligosaccharides from lactulose with a conversion ratio of 21.9% (w/w). Moreover, the enzyme catalyzed the synthesis of galacto-oligosaccharides from low-content lactose in fresh milk, and the GOS conversion ratios of 17.1% (w/w) and 7.8% (w/w) were obtained when the reactions were performed at 45 and 4 °C, respectively. These properties make PbBgal35A an ideal candidate for commercial use in the manufacturing of GOS-enriched dairy products.

A novel NIR fluorescent probe for enhanced β-galactosidase detection and tumor imaging in ovarian cancer models

The advancement of biological imaging techniques critically depends on the development of novel near-infrared (NIR) fluorescent probes. In this study, we introduce a designed NIR fluorescent probe, NRO-βgal, which exhibits a unique off-on response mechanism to β-galactosidase (β-gal). Emitting a fluorescence peak at a wavelength of 670 nm, NRO-βgal showcases a significant Stokes shift of 85 nm, which is indicative of its efficient energy transfer and minimized background interference. The probe achieves a remarkably low in vitro detection limit of 0.2 U/L and demonstrates a rapid response within 10 min, thereby underscoring its exceptional sensitivity, selectivity, and operational swiftness. Such superior analytical performance broadens the horizon for its application in intricate biological imaging studies. To validate the practical utility of NRO-βgal in bio-imaging, we employed ovarian cancer cell and mouse models, where the probe's efficacy in accurately delineating tumor cells was examined. The results affirm NRO-βgal's capability to provide sharp, high-contrast images of tumor regions, thereby significantly enhancing the precision of surgical tumor resection. Furthermore, the probe's potential for real-time monitoring of enzymatic activity in living tissues underscores its utility as a powerful tool for diagnostics in oncology and beyond.

Engineering the β-galactosidase from Aspergillus oryzae for making lactose-free and no-sugar-added yogurt

Yogurt usually contains 5% to 7% sugar and 3% to 5% lactose. As β-galactosidases can hydrolyze lactose and improve sweetness, they have the potential to produce lactose-free (LF) and no-sugar-added (NSA) yogurt. In this study, the β-galactosidase AoBgal35A from Aspergillus oryzae was engineered by site-saturation mutagenesis. Results of 19 variants of T955 residue showed that the lactose hydrolysis rate of T955R-AoBgal35A was up to 90.7%, which is much higher than the 78.5% of the wild type. Moreover, the optimal pH of T955R-AoBgal35A was shifted from pH 4.5 to pH 5.5, and the optimal temperature decreased from 60°C to 50°C. The mutant T955R-AoBgal35A was successfully expressed in Komagataella pastoris, which produced extracellularly 4,528 U/mL of β-galactosidase activity. The mutant T955R-AoBgal35A was used to produce LF yogurt. The Streptococcus thermophilus count of LF yogurt increased from 7.9 to 9.5 log cfu/g, which is significantly higher than that of the control group (8.9 log cfu/g). The residual lactose content of LF yogurt was 0.13%, meeting the requirements of the national standard in China for the "lactose-free" label (<0.5%). Furthermore, sugar in yogurt was replaced by whey powder to produce LF-NSA yogurt. The optimal addition content of whey powder was 7.5%. The texture, water-holding capacity, and titratable acidity of LF and LF-NSA yogurt achieved good shelf life stability. Therefore, this study provides an insight for technological implications of β-galactosidases in the dairy industry.

Aspergillus oryzae β-D-galactosidase immobilization on glutaraldehyde pre-activated amino-functionalized magnetic mesoporous silica: Performance, characteristics, and application in the preparation of sesaminol

Aspergillus oryzae β-D-galactosidase (β-Gal) efficiently hydrolyzes sesaminol triglucoside into sesaminol, which has higher biological activity. However, β-Gal is difficult to be separate from the reaction mixture and limited by stability. To resolve these problems, β-Gal was immobilized on amino-functionalized magnetic nanoparticles mesoporous silica pre-activated with glutaraldehyde (Fe3O4@mSiO2-β-Gal), which was used for the first time to prepare sesaminol. Under the optimal conditions, the immobilization yield and recovered activity of β-Gal were 57.9 ± 0.3 % and 46.5 ± 0.9 %, and the enzymatic loading was 843 ± 21 Uenzyme/gsupport. The construction of Fe3O4@mSiO2-β-Gal was confirmed by various characterization methods, and the results indicated it was suitable for heterogeneous enzyme-catalyzed reactions. Fe3O4@mSiO2-β-Gal was readily separable under magnetic action and displayed improved activity in extreme pH and temperature conditions. After 45 days of storage at 4 °C, the activity of Fe3O4@mSiO2-β-Gal remained at 92.3 ± 2.8 %, which was 1.29 times than that of free enzyme, and its activity remained above 85 % after 10 cycles. Fe3O4@mSiO2-β-Gal displayed higher affinity and catalytic efficiency. The half-life was 1.41 longer than free enzymes at 55.0 °C. Fe3O4@mSiO2-β-Gal was employed as a catalyst to prepare sesaminol, achieving a 96.7 % conversion yield of sesaminol. The excellent stability and catalytic efficiency provide broad benefits and potential for biocatalytic industry applications.

Physiologically Aggregated LacZ Applied in Trehalose Galactosylation in a Recycled Batch Mode

Galactooligosaccharides obtained via β-galactosidase transgalactosylation have health-promoting properties and are widely recognized as effective prebiotics. Trehalose-based galactooligosaccharides could be introduced into food and pharmaceutical industries similarly to trehalose. In light of this, new technological approaches are needed. Recently, in vivo enzyme immobilizations for recombinant proteins have been introduced, and physiological aggregation into active inclusion bodies (aIBs) has emerged as one such method of in vivo immobilization. To prepare LacZ β-galactosidase in the form of aIBs, we used a short 10 amino acid aggregation-prone tag. These native protein particles were simply washed from the cell lysate and applied in trehalose galactosylation in a recycled batch mode. In this study, aIBs entrapped in alginate beads, encapsulated in alginate/cellulose sulfate/poly(methylene-co-guanidine) capsules and magnetized were compared with free aIBs. Alginate/cellulose sulfate/PMCG capsules showed more suitable properties and applicability for biotransformation of trehalose at its high concentration (25%, w/v) and elevated temperature (50 °C).

Chaperonin GroEL hydrolyses ortho-nitrophenyl β-galactoside

We serendipitously found that chaperonin GroEL can hydrolyze ortho-nitrophenyl β-galactoside (ONPG), a well-known substrate of the enzyme β-galactosidase. The ONPG hydrolysis by GroEL follows typical enzyme kinetics. Our experiments and molecular docking studies suggest ONPG binding at the ATP binding site of GroEL.

Isolation of Pseudomonas oleovorans Carrying Multidrug Resistance Proteins MdtA and MdtB from Wastewater

The pollution of industrial wastewater has become a global issue in terms of economic development and ecological protection. Pseudomonas oleovorans has been studied as a bacterium involved in the treatment of petroleum pollutants. Our study aimed to investigate the physicochemical properties and drug resistance of Pseudomonas oleovorans isolated from industrial wastewater with a high concentration of sulfate compounds. Firstly, Pseudomonas oleovorans was isolated and then identified using matrix-assisted flight mass spectrometry and 16S rDNA sequencing. Then, biochemical and antibiotic resistance analyses were performed on the Pseudomonas oleovorans, and a microbial high-throughput growth detector was used to assess the growth of the strain. Finally, PCR and proteomics analyses were conducted to determine drug-resistance-related genes/proteins. Based on the results of the spectrum diagram and sequencing, the isolated bacteria were identified as Pseudomonas oleovorans and were positive to reactions of ADH, MTE, CIT, MLT, ONPG, and ACE. Pseudomonas oleovorans was sensitive to most of the tested antibiotics, and its resistance to SXT and CHL and MIN and TIM was intermediate. The growth experiment showed that Pseudomonas oleovorans had a good growth rate in nutrient broth. Additionally, gyrB was the resistance gene, and mdtA2, mdtA3, mdtB2, mdaB, and emrK1 were the proteins that were closely associated with the drug resistance of Pseudomonas oleovorans. Our results show the biochemical properties of Pseudomonas oleovorans from industrial wastewater with a high concentration of sulfate compounds and provide a new perspective for Pseudomonas oleovorans to participate in biological removal of chemical pollutants in industrial wastewater.

Advances in Low-Lactose/Lactose-Free Dairy Products and Their Production

With increasing health awareness worldwide, lactose intolerance has become a major concern of consumers, creating new market opportunities for low-lactose/lactose-free dairy foods. In recent years, through innovating processes and technologies, dairy manufacturers have significantly improved the variety, and functional and sensory qualities of low-lactose and lactose-free dairy products. Based on this, this paper first covers the pathology and epidemiology of lactose intolerance and market trends. Then, we focus on current advantages and disadvantages of different lactose hydrolysis technologies and improvements in these technologies to enhance nutritional value, and functional, sensory, and quality properties of lactose-free dairy products. We found that more and more cutting-edge technologies are being applied to the production of lactose-free dairy products, and that these technologies greatly improve the quality and production efficiency of lactose-free dairy products. Hopefully, our review can provide a theoretical basis for the marketing expansion and consumption guidance for low-lactose/lactose-free dairy products.

Properties and biotechnological applications of microbial deacetylase

Deacetylases, a class of enzymes that can catalyze the hydrolysis of acetylated substrates to remove the acetyl group, used in producing various products with high qualities, are one of the most influential industrial enzymes. These enzymes are highly specific, non-toxic, sustainable, and eco-friendly biocatalysts. Deacetylases and deacetylated compounds have been widely applicated in pharmaceuticals, medicine, food, and the environment. This review synthetically summarizes deacetylases' sources, characterizations, classifications, and applications. Moreover, the typical structural characteristics of deacetylases from different microbial sources are summarized. We also reviewed the deacetylase-catalyzed reactions for producing various deacetylated compounds, such as chitosan-oligosaccharide (COS), mycothiol, 7-aminocephalosporanic acid (7-ACA), glucosamines, amino acids, and polyamines. It is aimed to expound on the advantages and challenges of deacetylases in industrial applications. Moreover, it also serves perspectives on obtaining promising and innovative biocatalysts for enzymatic deacetylation. KEYPOINTS: • The fundamental properties of microbial deacetylases of various microorganisms are presented. • The biochemical characterizations, structures, and catalyzation mechanisms of microbial deacetylases are summarized. • The applications of microbial deacetylases in food, pharmaceutical, medicine, and the environment were discussed.

Targeted gene manipulation of Leloir pathway genes for the constitutive expression of β-galactosidase and its transgalactosylation product galacto-oligosaccharides from Kluyveromyces lactis GG799 and knockout strains

Galacto-oligosaccharides (GOS) are used as prebiotic ingredients in various food and pharmaceutical industry. At present, production of GOS involves the enzymatic transformation of lactose by transgalactosylation using β-galactosidase. The yeast Kluyveromyces lactis can utilize lactose as its carbon and energy source. In this species lactose is hydrolyzed by an intracellular β-galactosidase (EC 3.2.1.23) which is induced by its substrate and related compounds like galactose. The molecular details of gene regulation in kluyveromyces lactis, we have used multiple knockout approaches to study the constitutive expression by which galactose induces β-galactosidase. The present study involved carrying out to a method of enhancing the constitutive expression of β-galactosidase through galactose induction and its trans-galactosylation reaction for the production of galacto-oligosaccharides (GOS) in Kluyveromyces lactis (K. Lactis) by applying a knockout based approach on Leloir pathway genes based on fusion-overlap extension polymerase chain reaction and transformation into its genome. The k.lactis strain subjected to Leloir pathway genes knockout, resulted in the accumulation of galactose intracellularly and this internal galactose acts as an inducer of galactose regulon for constitutive expression of β-galactosidase at early stationary phase was due to the positive regulatory function of mutant gal1p, gal7p and both. These resulted strains used for trans-galactosylation of lactose by β - galactosidase is characterized for the production of galacto-oligosaccharides. Galactose-induced constitutive expression of β-galactosidase during the early stationary phase of knockout strains was analysed qualitatively & quantitatively. The activity of β-galactosidase of wild type, gal1z, gal7k and gal1z & gal7k strains were 7, 8, 9 and 11 U/ml respectively using high cell density cultivation medium. Based on these expression differences in β-galactosidase, the trans-galactosylation reaction for GOS production and percentage yield of GOS were compared at 25% w/v of lactose. The percentage yield of GOS production of wild type, Δgal1z Lac4+, Δgal7k Lac4++ and Δgal1z Δgal7k Lac4+++mutants strains were 6.3, 13, 17 and 22 U/ml, respectively. Therefore, we propose that the availability of galactose can be used for constitutive over expression of β - galactosidase in Leloir pathway engineering applications and also for GOS production. Further, increased expression of β - galactosidases can be used in dairy industry by-products like whey to produce added value products such as galacto-oligosaccharides.

A dual-signal fluorometric and colorimetric sensing platform based on gold-platinum bimetallic nanoclusters for the determination of β-galactosidase activity

Herein, a novel dual-signal sensing system for the determination of β-galactosidase (β-Gal) activity was established, which was based on a dual-emission probe assembled from gold-platinum bimetallic nanoclusters (Au-Pt NCs) and rhodamine B. Under the catalysis of β-Gal, 4-nitrophenyl β-D-galactopyranoside (PNPG) was rapidly hydrolyzed to generate p-nitrophenol (PNP), which has an obvious UV absorption peak at 400 nm. The hydrolyzed product PNP can quench the fluorescence of Au-Pt NCs effectively by inner filter effect (IFE), and PNP had no impact on the fluorescence of rhodamine B, which will change the emission intensity ratio of Au-Pt NCs and rhodamine B. Therefore, the ratiometric fluorescent and colorimetric dual-signal sensor based on Au-Pt NCs and rhodamine B was successfully constructed for sensitive detection of β-Gal activity. The linear detection range for the ratiometric fluorescence and colorimetric methods were 2.5-25 U/L and 15-55 U/L with detection limits of 1.2 U/L and 5.2 U/L, respectively. The developed assay method has been used for quantitative detection of β-Gal in spiked serum samples and showed good performance. And the detection platform has high reliability and excellent selectivity, which opens a new avenue for the further application of Au-Pt NCs in chemical sensing and biological analysis.

Use of soil actinomycetes for pharmaceutical, food, agricultural, and environmental purposes

In this article, we reviewed the international scientific production of the last years on actinomycetes isolated from soil aiming to report recent advances in using these microorganisms for different applications. The most promising genera, isolation conditions and procedures, pH, temperature, and NaCl tolerance of these bacteria were reported. Based on the content analysis of the articles, most studies have focused on the isolation and taxonomic description of new species of actinomycetes. Regarding the applications, the antimicrobial potential (antibacterial and antifungal) prevailed among the articles, followed by the production of enzymes (cellulases and chitinases, etc.), agricultural uses (plant growth promotion and phytopathogen control), bioremediation (organic and inorganic contaminants), among others. Furthermore, a wide range of growth capacity was verified, including temperatures from 4 to 60 °C (optimum: 28 °C), pH from 3 to 13 (optimum: 7), and NaCl tolerance up to 32% (optimum: 0-1%), which evidence a great tolerance for actinomycetes cultivation. Streptomyces was the genus with the highest incidence among the soil actinomycetes and the most exploited for different uses. Besides, the interest in isolating actinomycetes from soils in extreme environments (Antarctica and deserts, for example) is growing to explore the adaptive capacities of new strains and the secondary metabolites produced by these microorganisms for different industrial interests, especially for pharmaceutical, food, agricultural, and environmental purposes.

A novel salt-tolerant GH42 β-galactosidase with transglycosylation activity from deep-sea metagenome

β-Galactosidase is a widely adopted enzyme in the food and pharmaceutical industries. Metagenome techniques have the advantage of discovering novel functional genes, particularly potential genes from uncultivated microbes. In this study, a novel GH42 β-galactosidase isolated from a deep-sea metagenome was overexpressed in Escherichia coli BL21 (DE3) and purified by affinity chromatography. The optimal temperatures and pH of the enzyme for o-nitrophenyl-β-D-galactopyranoside (oNPG) and lactose were 40 ℃, 6.5 and 50 ℃, 7, respectively. The enzyme was stable at temperatures between 4 and 30 ℃ and within the pH range of 6-9. Moreover, it was highly tolerant to salt and inhibited by Zn²⁺ and Cu²⁺. The kinetic values of K_m and k_cat of the enzyme against oNPG were 1.1 mM and 57.8 s^-1, respectively. Furthermore, it showed hydrolysis and transglycosylation activity to lactose and the extra monosaccharides could improve the productivity of oligosaccharides. Overall, this recombinant β-galactosidase is a potential biocatalyst for the hydrolysis of milk lactose and synthesis of functional oligosaccharides.

An acid-tolerant and cold-active β-galactosidase potentially suitable to process milk and whey samples

A novel β-galactosidase gene (gal_M) was cloned from an aquatic habitat metagenome. The analysis of its translated sequence (Gal_M) revealed its phylogenetic closeness towards Verrucomicrobia sp. The sequence comparison and homology structure analysis designated it a member of GH42 family. The three-dimensional homology model of Gal_M depicted a typical (β/α)8 TIM-barrel containing the catalytic core. The gene (gal_M) was expressed in a heterologous host, Escherichia coli, and the purified protein (Gal_M) was subjected to biochemical characterization. It displayed β-galactosidase activity in a wide range of pH (2.0 to 9.0) and temperature (4 to 60 °C). The heat exposed protein showed considerable stability at 40 and 50 °C, with the half-life of about 100 h and 35 h, respectively. The presence of Na, Mg, K, Ca, and Mn metals was favorable to the catalytic efficiency of Gal_M, which is a desirable catalytic feature, as these metals exist in milk. It showed remarkable tolerance of glucose and galactose in the reaction. Furthermore, Gal_M discerned transglycosylation activity that is useful in galacto-oligosaccharides' production. These biochemical properties specify the suitability of this biocatalyst for milk and whey processing applications. KEY POINTS: • A novel β-galactosidase gene was identified and characterized from an aquatic habitat. • It was active in extreme acidic to mild alkaline pH and at cold to moderate temperatures. • The β-galactosidase was capable to hydrolyze lactose in milk and whey.