Cloning, purification, and characterization of β-galactosidase from Bacillus licheniformis DSM 13

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%.

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 engineered genetic circuit for lactose intolerance alleviation

BACKGROUND

Lactose malabsorption occurs in around 68% of the world's population, causing lactose intolerance (LI) symptoms, such as abdominal pain, bloating, and diarrhea. To alleviate LI, previous studies have mainly focused on strengthening intestinal β-galactosidase activity while neglecting the inconspicuous drop in the colon pH caused by the fermentation of non-hydrolyzed lactose by the gut microbes. A drop in colon pH will reduce the intestinal β-galactosidase activity and influence intestinal homeostasis.

RESULTS

Here, we synthesized a tri-stable-switch circuit equipped with high β-galactosidase activity and pH rescue ability. This circuit can switch in functionality between the expression of β-galactosidase and expression of L-lactate dehydrogenase in response to an intestinal lactose signal and intestinal pH signal, respectively. We confirmed that the circuit functionality was efficient in bacterial cultures at a range of pH levels, and in preventing a drop in pH and β-galactosidase activity after lactose administration to mice. An impact of the circuit on gut microbiota composition was also indicated.

CONCLUSIONS

Due to its ability to flexibly adapt to environmental variation, in particular to stabilize colon pH and maintain β-galactosidase activity after lactose influx, the tri-stable-switch circuit can serve as a promising prototype for the relief of lactose intolerance.

Overexpression and characterization of a novel GH4 galactosidase with β-galactosidase activity from Bacillus velezensis SW5

A novel galactosidase gene (gal3149) was identified from Bacillus velezensis SW5 and heterologously expressed in Escherichia coli BL21 (DE3). The novel galactosidase, Gal3149, encoded by gal3149 in an open reading frame of 1,299 bp, was 433 amino acids in length. Protein sequence analysis showed that Gal3149 belonged to family 4 of glycoside hydrolases (GH4). Gal3149 displayed higher enzyme activity for the substrate 2-nitrophenyl-β-d-galactopyranoside (oNPG) than for 4-nitrophenyl-α-d-galactopyranoside (pNPαG). This is the first time that an enzyme belonging to GH4 has been shown to exhibit β-galactosidase activity. Gal3149 showed optimal activity at pH 8.0 and 50°C, and exhibited excellent thermal stability, with retention of 50% relative activity after incubation at a temperature range of 0 to 50°C for 48 h. Gal3149 activity was significantly improved by K⁺ and Na⁺, and was strongly or completely inhibited by Ag⁺, Zn²⁺, Tween-80, Cu²⁺, carboxymethyl cellulose, and oleic acid. The rate of hydrolyzed lactose in 1 mL of milk by 1 U of Gal3149 reached about 50% after incubation for 4 h. These properties lay a solid foundation for Gal3149 in application of the lactose-reduced dairy industry.

Immobilization of β-galactosidase from Bacillus licheniformis for application in the dairy industry

The food industry has developed a wide range of products with reduced lactose to allow people with intolerance to consume dairy products. Although β-galactosidase has extensive applications in the food, pharma, and biotechnology industries, the enzymes are high-cost catalysts, and their use makes the process costly. Immobilization is a viable strategy for enzyme retention inside a reactor, allowing its reuse and application in continuous processes. Here, we studied the immobilization of β-galactosidase from Bacillus licheniformis in ion exchange resin. A central composite rotational design (CCRD) was proposed to evaluate the immobilization process in relation to three immobilization solution variables: offered enzyme activity, ionic strength, and pH. The conditions that maximized the response were offered enzyme activity of 953 U, 40 mM ionic strength, and pH 4.0. Subsequently, experiments were performed to provide additional stabilization for biocatalyst, using a buffer solution pH 9.0 at 25 °C for 24 h, and crosslinking with different concentrations of glutaraldehyde. The stabilization step drastically impacted the activity of the immobilized enzyme, and the reticulation with different concentrations of glutaraldehyde showed significant influence on the activity of the immobilized enzyme. In spite of substantially affecting the initial activity of the immobilized enzyme, higher reagent concentrations (3.5 g L^-1) were effective for maintaining stability related to the number of cycles of the enzyme immobilized. The β-galactosidase from Bacillus licheniformis immobilized in Duolite A568 is a promising technique to produce reduced or lactose-free dairy products, as it allows reuse of the biocatalyst, decreasing operational costs.Key Points• Immobilization of β-galactosidase from Bacillus licheniformis in batch reactor• Influence of buffer pH and ionic concentration and offered enzyme activity on immobilization• Influence of glutaraldehyde on operational stability.

Construction and Evaluation of Peptide-Linked Lactobacillus brevis β-Galactosidase Heterodimers

BACKGROUND

β-galactosidases are enzymes that are utilized to hydrolyze lactose into galactose and glucose, and are is widely used in the food industry.

OBJECTIVE

We describe the recombinant expression of an unstudied, heterodimeric β-galactosidase originating from Lactobacillus brevis ATCC 367 in Escherichia coli. Furthermore, six different constructs, in which the two protein subunits were fused with different peptide linkers, were also investigated.

METHODS

The heterodimeric subunits of the β-galactosidase were cloned in expressed in various expression constructs, by using either two vectors for the independent expression of each subunit, or using a single Duet vector for the co-expression of the two subunits.

RESULTS

The co-expression in two independent expression vectors only resulted in low β-galactosidase activities, whereas the co-expression in a single Duet vector of the independent and fused subunits increased the β-galactosidase activity significantly. The recombinant β-galactosidase showed comparable hydrolyzing properties towards lactose, N-acetyllactosamine, and pNP-β-D-galactoside.

CONCLUSION

The usability of the recombinant L. brevis β-galactosidase was further demonstrated by the hydrolysis of human, bovine, and goat milk samples. The herein presented fused β-galactosidase constructs may be of interest for analytical research as well as in food- and biotechnological applications.

β-Galactosidase: From its source and applications to its recombinant form

Carbohydrate-active enzymes are a group of important enzymes playing a critical role in the degradation and synthesis of carbohydrates. Glycosidases can hydrolyze glycosides into oligosaccharides, polysaccharides, and glycoconjugates via a cost-effective approach. Lactase is an important member of β-glycosidases found in higher plants, animals, and microorganisms. β-Galactosidases can be used to degrade the milk lactose for making lactose-free milk, which is sweeter than regular milk and is suitable for lactose-intolerant people. β-Galactosidase is employed by many food industries to degrade lactose and improve the digestibility, sweetness, solubility, and flavor of dairy products. β-Galactosidase enzymes have various families and are applied in the food-processing industries such as hydrolyzed-milk products, whey, and galactooligosaccharides. Thus, this enzyme is a valuable protein which is now produced by recombinant technology. In this review, origins, structure, recombinant production, and critical modifications of β-galactosidase for improving the production process are discussed. Since β-galactosidase is a valuable enzyme in industry and health care, a study of its various aspects is important in industrial biotechnology and applied biochemistry.

Cloning, expression, and bioinformatics analysis and characterization of a β-galactosidase from Bacillus coagulans T242

The activities of β-galactosidases from bacteria and molds are affected by temperature, pH, and other factors in the processing of dairy products, limiting their application, so it is necessary to find alternative lactases. In this study, the β-galactosidase gene from Bacillus coagulans T242 was cloned, co-expressed with a molecular chaperone in Escherichia coli BL21, and subjected to bioinformatic and kinetic analyses and lactase characterization. The results show that the enzyme is a novel thermostable neutral lactase with optimum hydrolytic activity at pH 6.8 and 50°C. The thermal stability and increased lactose hydrolysis activity of β-galactosidase in the presence of Ca²⁺ indicated its potential application in the dairy industry.

Activation of LacZ gene in Escherichia coli DH5α via α-complementation mechanism for β-galactosidase production and its biochemical characterizations

Background

Plasmid propagation in recombination strains such as Escherichia coli DH5α is regarded as a beneficial instrument for stable amplification of the DNA materials. Here, we show trans-conjugation of pGEM-T cloning vector (modified Promega PCR product cloning vector with tra genes, transposable element (Tn5)) and M13 sequence via α-complementation mechanism in order to activate β-d-galactosidase gene in DH5α strain (non-lactose-fermenting host).

Results

Trans-conjugation with pGEM-T allows correction of LacZ gene deletion through Tn5, and successful trans-conjugants in DH5α host cells can be able to produce active enzyme, thus described as lactose fermenting strain. The intracellular β-galactosidase was subjected to precipitation by ammonium sulfate and subsequently gel filtration, and the purified enzyme showed a molecular weight of approximately 72-kDa sodium dodecyl sulfate-polyacrylamid gel electrophoresis. The purified enzyme activity showed an optimal pH and temperature of 7.5 and 40 °C, respectively; it had a high stability within pH 6–8.5 and moderate thermal stability up to 50 °C.

Conclusion

Trans-conjugant of E. coli DH5α- lacZ∆M15 was successfully implemented. UV mutagenesis of the potent trans-conjugant isolate provides an improvement of the enzyme productivity. The enzymatic competitive inhibition by d-galactose and hydrolysis of lactose at ambient temperatures could make this enzyme a promising candidate for use in the dairy industry.

The Butyrogenic and Lactic Bacteria of the Gut Microbiota Determine the Outcome of Allogenic Hematopoietic Cell Transplant

Graft versus host disease (GVHD) is a post-transplant pathology in which donor-derived T cells present in the Peyer's patches target the cell-surface alloantigens of the recipient, causing host tissue damages. Therefore, the GVHD has long been considered only a purely immunological process whose prevention requires an immunosuppressive treatment. However, since the early 2010s, the impact of gut microbiota on GVHD has received increased attention. Both a surprising fall in gut microbiota diversity and a shift toward Enterobacteriaceae were described in this disease. Recently, unexpected results were reported that further link GVHD with changes in bacterial composition in the gut and disruption of intestinal epithelial tight junctions leading to abnormal intestinal barrier permeability. Patients receiving allogenic hematopoietic stem cell transplant (allo-HCT) as treatment of hematologic malignancies showed a decrease of the overall diversity of the gut microbiota that affects Clostridia and Blautia spp. and a predominance of lactic acid bacteria (LAB) of the Enterococcus genus, in particular the lactose auxotroph Enterococcus faecium. The reduced microbiota diversity (likely including Actinobacteria, such as Bifidobacterium adolescentis that cross feed butyrogenic bacteria) deprives the butyrogenic bacteria (such as Roseburia intestinalis or Eubacterium) of their capacity to metabolize acetate to butyrate. Indeed, administration of butyrate protects against the GVHD. Here, we review the data highlighting the possible link between GVHD and lactase defect, accumulation of lactose in the gut lumen, reduction of Reg3 antimicrobial peptides, narrower enzyme equipment of bacteria that predominate post-transplant, proliferation of En. faecium that use lactose as metabolic fuels, induction of innate and adaptive immune response against these bacteria which maintains an inflammatory process, elevated expression of myosin light chain kinase 210 (MLCK210) and subsequent disruption of intestinal barrier, and translocation of microbial products (lactate) or transmigration of LAB within the liver. The analysis of data from the literature confirms that the gut microbiota plays a major role in the GVHD. Moreover, the most recent publications uncover that the LAB, butyrogenic bacteria and bacterial cross feeding were the missing pieces in the puzzle. This opens new bacteria-based strategies in the treatment of GVHD.

Cloning and Characterization of a New β-Galactosidase from Alteromonas sp. QD01 and Its Potential in Synthesis of Galacto-Oligosaccharides

As prebiotics, galacto-oligosaccharides (GOSs) can improve the intestinal flora and have important applications in medicine. β-galactosidases could promote the synthesis of GOSs in lactose and catalyze the hydrolysis of lactose. In this study, a new β-galactosidase gene (gal2A), which belongs to the glycoside hydrolase family 2, was cloned from marine bacterium Alteromonas sp. QD01 and expressed in Escherichia coli. The molecular weight of Gal2A was 117.07 kDa. The optimal pH and temperature of Gal2A were 8.0 and 40 °C, respectively. At the same time, Gal2A showed wide pH stability in the pH range of 6.0–9.5, which is suitable for lactose hydrolysis in milk. Most metal ions promoted the activity of Gal2A, especially Mn²⁺ and Mg²⁺. Importantly, Gal2A exhibited high transglycosylation activity, which can catalyze the formation of GOS from milk and lactose. These characteristics indicated that Gal2A may be ideal for producing GOSs and lactose-reducing dairy products.

The co-existence of cold activity and thermal stability in an Antarctic GH42 β-galactosidase relies on its hexameric quaternary arrangement

To survive in cold environments, psychrophilic organisms produce enzymes endowed with high specific activity at low temperature. The structure of these enzymes is usually flexible and mostly thermolabile. In this work, we investigate the structural basis of cold adaptation of a GH42 β-galactosidase from the psychrophilic Marinomonas ef1. This enzyme couples cold activity with astonishing robustness for a psychrophilic protein, for it retains 23% of its highest activity at 5 °C and it is stable for several days at 37 °C and even 50 °C. Phylogenetic analyses indicate a close relationship with thermophilic β-galactosidases, suggesting that the present-day enzyme evolved from a thermostable scaffold modeled by environmental selective pressure. The crystallographic structure reveals the overall similarity with GH42 enzymes, along with a hexameric arrangement (dimer of trimers) not found in psychrophilic, mesophilic, and thermophilic homologues. In the quaternary structure, protomers form a large central cavity, whose accessibility to the substrate is promoted by the dynamic behavior of surface loops, even at low temperature. A peculiar cooperative behavior of the enzyme is likely related to the increase of the internal cavity permeability triggered by heating. Overall, our results highlight a novel strategy of enzyme cold adaptation, based on the oligomerization state of the enzyme, which effectively challenges the paradigm of cold activity coupled with intrinsic thermolability. DATABASE: Structural data are available in the Protein Data Bank database under the accession number 6Y2K.

Bacterial Lactase Gene Characteristics in Intestinal Contents of Antibiotic-Associated Diarrhea Mice Treated with Debaryomyces hansenii

Background

Debaryomyces hansenii exhibits a therapeutic effect on antibiotic-associated diarrhea (AAD) by promoting the growth of beneficial intestinal bacteria. Previous research has reported that AAD involves not only dysbacteriosis but also dysfunction of the activity of intestinal enzymes (such as lactase). Enzyme activities can be influenced by many other factors, such as gene expression. The present study showed that D. hansenii has a curative effect on AAD at the lactase gene level.

Material/Methods

The effect of D. hansenii on the lactase gene from intestinal bacteria in AAD mice was investigated. The diarrhea model was established with a gentamycin sulfate and cefradine capsule mixture. The antibiotic mixture (23.33 mL·kg⁻¹·day⁻¹) was intragastrically administered for 5 days. Subsequently, half of the diarrhea mice were treated with D. hansenii twice a day for 3 days while the other mice were intragastrically administered with the same volume of distilled water. Next, the intestinal contents were collected, and metagenomic DNA was extracted for high-throughput sequencing analysis.

Results

The Chao1 and Shannon indices decreased significantly following treatment with D. hansenii (P<0.01 and P<0.05, respectively). Moreover, the clusters in the D. hansenii group mice were quite different from those in the normal group mice and model group mice. Following treatment with D. hansenii, the quantity of lactase genes in Enterobacter sp. 638 and Modestobacter increased markedly, and the richness of intestinal bacterial lactase genes in Fretibacterium recovered.

Conclusions

D. hansenii altered the lactase-producing bacterial community structure and promoted the growth of several critical lactase-producing bacteria, such as Enterobacter sp. 638 and Modestobacter.

Characterization of three novel β-galactosidases from Akkermansia muciniphila involved in mucin degradation

The gut microbe Akkermansia (A.) muciniphila becomes increasingly important as its prevalence is inversely correlated with different human metabolic disorders and diseases. This organism is a highly potent degrader of intestinal mucins and the hydrolyzed glycan compounds can then serve as carbon sources for the organism itself or other members of the gut microbiota via cross-feeding. Despite its importance for the hosts' health and microbiota composition, exact mucin degrading mechanisms are still mostly unclear. In this study, we identified and characterized three extracellular β-galactosidases (Amuc_0771, Amuc_0824, and Amuc_1666) from A. muciniphila ATCC BAA-835. The substrate spectrum of all three enzymes was analyzed and the results indicated a preference for different galactosidic linkages for each hydrolase. All preferred target structures are prevalent within mucins of the colonic habitat of A. muciniphila. To check a potential function of the enzymes for the degradation of mucosal glycan structures, porcine stomach mucin was applied as a model substrate. In summary, we could confirm the involvement of all three β-galactosidases from A. muciniphila in the complex mucin degradation machinery of this important gut microbe. These findings could contribute to the understanding of the molecular interactions between A. muciniphila and its host on a molecular level.

Quantification of the α2-6 Sialic Acid Linkage in Branched N-Glycan Structures with Capillary Nanogel Electrophoresis

Sialylation and sialic acid linkage in N-glycans are markers of disease but are analytically challenging to quantify. A capillary electrophoresis method is reported that integrates a unique combination of enzymes and lectins to modify sialylated N-glycans in real time in the capillary so that N-glycan structures containing α2-6-linked sialic acid are easily separated, detected, and quantified. In this study, N-glycans were sequentially cleaved by enzymes at the head of the separation capillary so that the presence of α2-6-linked sialic acids corresponded to a shift in the analyte migration time in a manner that enabled interpretation of the N-glycan structure. Following injection, only afucosylated N-glycan structures were passed through enzyme zones that contained α2-3 sialidase, followed by β1-3,4 galactosidase, which cleaved any terminal α2-3-linked sialic acid and underlying galactose yielding a terminal N-acetyl glucosamine. With this treatment complete, a third zone of α2-3,6,8 sialidase converted the remaining α2-6-linked sialic acid to terminal galactose. With these enzyme processing steps the α2-6-linked sialic acid residues on an N-glycan correlated directly to the number of terminal galactose residues that remained. The number of terminal galactose residues could be interpreted as a stepwise decrease in the migration time. Complex N-glycans from α-1-acid glycoprotein were analyzed using this approach, revealing that a limited number of α2-6-linked sialic acids were present with biantennary, triantennary, and tetraantennary N-glycans of α-1-acid glycoprotein generally containing 0 or 1 α2-6-linked sialic acid.

A New β-Galactosidase from the Antarctic Bacterium Alteromonas sp. ANT48 and Its Potential in Formation of Prebiotic Galacto-Oligosaccharides

As an important medical enzyme, β-galactosidases catalyze transgalactosylation to form prebiotic Galacto-Oligosaccharides (GOS) that assist in improving the effect of intestinal flora on human health. In this study, a new glycoside hydrolase family 2 (GH2) β-galactosidase-encoding gene, galA, was cloned from the Antarctic bacterium Alteromonas sp. ANT48 and expressed in Escherichia coli. The recombinant β-galactosidase GalA was optimal at pH 7.0 and stable at pH 6.6–7.0, which are conditions suitable for the dairy environment. Meanwhile, GalA showed most activity at 50 °C and retained more than 80% of its initial activity below 40 °C, which makes this enzyme stable in normal conditions. Molecular docking with lactose suggested that GalA could efficiently recognize and catalyze lactose substrates. Furthermore, GalA efficiently catalyzed lactose degradation and transgalactosylation of GOS in milk. A total of 90.6% of the lactose in milk could be hydrolyzed within 15 min at 40 °C, and the GOS yield reached 30.9%. These properties make GalA a good candidate for further applications.

Purification and catalytic behavior optimization of lactose degrading β-galactosidase from Aspergillus nidulans

The β-galactosidase is an industrially valuable enzyme and used to hydrolyze the lactose into glucose and galactose. Considering the broad utility profile in food industry, β-galactosidase from Aspergillus nidulans was purified and characterized in term of its catalytic properties and stability. It displayed highest catalytic efficiency at 60 °C after 10.0 min within acidic pH environment (pH 5). The β-galactosidase exhibited 100% and 60% catalytic activity at 40 °C and 50 °C, respectively even after 120.0 min. The β-galactosidase activity was remained stable in the presence of Zn²⁺, Ni²⁺, and Mg²⁺ ions. The activity was also retained in all investigated organic solvents except DMSO at various ionic concentrations. The surfactants Triton X-100 and SDS caused positive impact on the catalytic activity of enzyme at 1.0 mM concentration. However, the percent relative activity of β-galactosidase was significantly reduced when incubated with EDTA. The molecular mass of β-galactosidase estimated to be 95 kDa. The SEM micrographs of ONPG before and after β-galactosidase treatment indicated a remarkable difference in the morphology and proved the strong catalytic strength of enzyme. The β-galactosidase also demonstrated exceptional storage stability at - 80 °C, - 20 °C and 4 °C by retaining 86, 79 and 70% activity even after 100.0 days.

Bacterial lactase genes diversity in intestinal mucosa of dysbacterial diarrhea mice treated with Qiweibaizhu powder

The current research tried to investigate the effect of Qiweibaizhu powder (QWBZP) on intestinal mucosa bacterial lactase gene from dysbacterial diarrhea mice, as the good therapeutic mechanism of QWBZP on antibiotics-induced diarrhea. Dysbacterial diarrhea mice model was constructed by gastric perfusion with mixture of cephradine capsules and gentamicin sulfate (23.33 mL kg-1 day-1) for 5 days. After the success of establishing diarrhea, the mice in treatment group were gavaged with QWBZP for 3 days. Intestinal mucosa in each group was collected, and diversity of bacterial lactase genes in intestinal mucosa of mice was carried out by Miseq metagenome sequencing. The results showed the Chao1, ACE, Simpson and Shannon indices in treatment group were lower than model group and were similar to control group. The same result was obtained from the operational taxonomic units (OTUs). There were 298, 435 and 254 OTUs in the control group, model group and treatment group, respectively. Principal component analysis (PCA) indicated that samples distribution in both normal and treatment groups were relatively intensive, distances among individuals were small, while opposite results were observed in model group. Moreover, antibiotics increased the diversity and abundance of bacterial lactase genes at phylum and genus levels. However, they decreased and were similar to control group after treating with QWBZP. Our results indicate that QWBZP has a positive effect on the recovery of bacterial lactase gene diversity to normal level. In addition, QWBZP increase the abundance of Lysobacter and Eukaryota.

Bacterial lactase genes diversity in intestinal mucosa of mice with dysbacterial diarrhea induced by antibiotics

The current study aimed at exploring the diversity of bacterial lactase genes in the intestinal mucosa of mice with dysbacterial diarrhea induced by antibiotics and to provide experimental basis for antibiotics-induced diarrhea. Mice model of dysbacterial diarrhea was established by gastric perfusion with mixture of cephradine capsules and gentamicin sulfate (23.33 mL kg-1 d-1), twice a day and continuously for 5 days. Intestinal mucosa from jejunum to ileum was collected, and bacterial metagenomic DNA was extracted for Miseq metagenome sequencing to carry out diversity analysis. The results showed that specific operational taxonomic units (OTUs) were 45 in the control group and 159 in the model group. The Chao1, ACE, Shannon and Simpson indices in model group were significantly higher (P < 0.01 or P < 0.05) than control group. Principal component analysis (PCA) and box chart of the control group were relatively intensive, while in the model group, they were widely dispersed. Furthermore, the inter-group box area was higher than that in the intra-group. Compared with the model group, the abundance of bacterial lactase genes in Proteobacteria from the intestinal mucosa of the control group was higher, but lower in Actinobacteria and unclassified bacteria. At the genus level, the relative abundance of bacterial species and taxon units in model group was obviously increased (P < 0.05). Our results indicate that antibiotics increased the diversity and abundance of bacterial lactase genes in the intestinal mucosa, as the abundance of Betaproteobacteria, Cupriavidus, Ewingella, Methyloversatilis, Rhodocyclaceae and Rhodocyclales. In addition, antibiotics become an additional source for lactase genes of Ewingella, Methyloversatilis, Mycobacterium, Microbacterium, Beutenberqia and Actinomyces.

Immunoprotective effect of traditional Chinese medicine on intestinal mucosa

The intestinal mucosa has a large surface area, contacts with the external antigens directly, and is the part exposed to most microbes. Growing evidence indicates that the relationship between intestinal mucosa and diseases is close. Traditional Chinese medicine is rich in a variety of bioactive ingredients and nutrients, which can provide energy and nutrition to maintain mucosal structure integrity and realize its physiological function, regulate intestinal flora directly or indirectly, establish intestinal mucosal immunity and barrier, and treat intestinal mucosal immune-related diseases. In this paper, we summarize the effect of traditional Chinese medicine on intestinal mucosal structure, immunity, flora, and metabolism, with an aim to provide some clues to the treatment of intestinal diseases using traditional Chinese medicine.

Diversity of bacterial lactase genes in intestinal contents of mice with antibiotics-induced diarrhea

AIM

To investigate the diversity of bacterial lactase genes in the intestinal contents of mice with antibiotics-induced diarrhea.

METHODS

Following 2 d of adaptive feeding, 12 specific pathogen-free Kunming mice were randomly divided into the control group and model group. The mouse model of antibiotics-induced diarrhea was established by gastric perfusion with mixed antibiotics (23.33 mL·kg^-1·d^-1) composed of gentamicin sulfate and cephradine capsules administered for 5 days, and the control group was treated with an equal amount of sterile water. Contents of the jejunum and ileum were then collected and metagenomic DNA was extracted, after which analysis of bacterial lactase genes using operational taxonomic units (OTUs) was carried out after amplification and sequencing.

RESULTS

OTUs were 871 and 963 in the model group and control group, respectively, and 690 of these were identical. There were significant differences in Chao1 and ACE indices between the two groups (P < 0.05). Principal component analysis, principal coordination analysis and nonmetric multidimensional scaling analyses showed that OTUs distribution in the control group was relatively intensive, and differences among individuals were small, while in the model group, they were widely dispersed and more diversified. Bacterial lactase genes from the intestinal contents of the control group were related to Proteobacteria, Actinobacteria, Firmicutes and unclassified bacteria. Of these, Proteobacteria was the most abundant phylum. In contrast, the bacterial population was less diverse and abundant in the model group, as the abundance of Bradyrhizobium sp. BTAi1, Agrobacterium sp. H13-3, Acidovorax sp. KKS102, Azoarcus sp. KH32C and Aeromonas caviae was lower than that in the control group. In addition, of the known species, the control group and model group had their own unique genera, respectively.

CONCLUSION

Antibiotics reduce the diversity of bacterial lactase genes in the intestinal contents, decrease the abundance of lactase gene, change the lactase gene strains, and transform their structures.

Biochemical characterization of a novel β-galactosidase from Paenibacillus barengoltzii suitable for lactose hydrolysis and galactooligosaccharides synthesis

A β-galactosidase gene (PbBGal2A) was cloned from Paenibacillus barengoltzii and expressed in Escherichia coli. The in silico analysis of the deduced amino acid sequences revealed that PbBGal2A shared the highest identity of 40% with the characterized glycoside hydrolase (GH) family 2 β-galactosidase from Actinobacillus pleuropneumoniae. The recombinant β-galactosidase (PbBGal2A) was purified with a molecular mass of 124.2kDa on SDS-PAGE. The optimal pH and temperature of PbBGal2A were determined to be pH 7.5 and 45°C, respectively. PbBGal2A was stable within pH 6.0-8.0 and up to 45°C. It completely hydrolyzed the lactose in milk and whey powder solution. In addition, PbBGal2A exhibited high transglycosylation activity and a maximum yield of 47.9% (w/w) for galactooligosaccharides (GOS) production was obtained in 8h at a lactose concentration of 350g/L. These properties make PbBGal2A an ideal candidate for commercial use in the production of lactose-free milk and GOS.

蔗糖酶-异麦芽糖酶缺乏与腹泻的研究进展

蔗糖酶-异麦芽糖酶(sucrase-isomaltase, SI)是蔗糖酶在肠道内最主要的存在形式, 是最丰富的肠道二糖酶, 其包含了所有的蔗糖酶活性, 大部分的异麦芽糖酶活性及60%-80%的麦芽糖酶活性. 蔗糖酶-异麦芽糖酶缺乏症(sucrase-isomaltase deficiency, SID)是由于该二糖酶缺乏导致二糖吸收不良, 肠道正常生理功能受损, 机体营养不良, 生长发育落后, 甚至产生危及生命的胃肠道症状. 其最主要的临床表现是腹泻. 临床上通过调整肠道SI活性来治疗腹泻, 并将SI活性用于临床诊断. 本文主要阐述SID与腹泻的关系、研究进程以及诊疗手段, 促进SI在药理方面的研究.

OmpA signal peptide leads to heterogenous secretion of B. subtilis chitosanase enzyme from E. coli expression system

The production of secreted recombinant proteins from E. coli is pivotal to the biotechnological industry because it reduces the cost of downstream processing. Proteins destined for secretion contain an N-terminal signal peptide that is cleaved by secretion machinery in the plasma membrane. The resulting protein is released in an active mature form. In this study, Bacillus subtilis chitosanase (Csn) was used as a model protein to compare the effect of two signal peptides on the secretion of heterologous recombinant protein. The results showed that the E. coli secretion machinery could recognize both native bacillus and E. coli signal peptides. However, only the native bacillus signal peptide could generate the same N-terminal sequence as in the wild type bacteria. When the recombinant Csn constructs contained the E. coli OmpA signal peptide, the secreted enzymes were heterogeneous, comprising a mixed population of secreted enzymes with different N-terminal sequences. Nevertheless, the E. coli OmpA signal peptide was found to be more efficient for high expression and secretion of bacillus Csn. These findings may be used to help engineer other recombinant proteins for secretory production in E. coli.

Signification of intestinal lactase in diagnosis and treatment of infantile diarrhea

Lactase, existing in animals and gut microbes, is a disaccharide enzyme. It is usually distributed in mammalian intestinal microvillus membrane surface and in intestinal contents. Most intestinal bacteria have the ability to produce lactase. However, the lack of lactase is common in the human population, and lactase deficiency (LD) is closely related to the occurrence of infantile diarrhea. When LD occurs or the lactase activity is inhibited, children are prone to abdominal distension, intestinal cramps, diarrhea and other symptoms. When this lasts a long time, it may cause malnutrition and growth retardation. Improving the intestinal lactase activity has been used to treat infantile diarrhea. Lactase activity and lactose detection has been used for clinical diagnosis.

A multifunctional thermophilic glycoside hydrolase from Caldicellulosiruptor owensensis with potential applications in production of biofuels and biochemicals

BACKGROUND

Thermophilic enzymes have attracted much attention for their advantages of high reaction velocity, exceptional thermostability, and decreased risk of contamination. Exploring efficient thermophilic glycoside hydrolases will accelerate the industrialization of biofuels and biochemicals.

RESULTS

A multifunctional glycoside hydrolase (GH) CoGH1A, belonging to GH1 family with high activities of β-d-glucosidase, exoglucanase, β-d-xylosidase, β-d-galactosidase, and transgalactosylation, was cloned and expressed from the extremely thermophilic bacterium Caldicellulosiruptor owensensis. The enzyme exerts excellent thermostability by retaining 100 % activity after 12-h incubation at 75 °C. The catalytic coefficients (k cat/K m) of the enzyme against pNP-β-D-galactopyranoside, pNP-β-D-glucopyranoside, pNP-β-D-cellobioside, pNP-β-D-xylopyranoside, and cellobiose were, respectively, 7450.0, 2467.5, 1085.4, 90.9, and 137.3 mM(-1) s(-1). When CoGH1A was supplemented at the dosage of 20 Ucellobiose g(-1) biomass for hydrolysis of the pretreated corn stover, comparing with the control, the glucose and xylose yields were, respectively, increased 37.9 and 42.1 %, indicating that the enzyme contributed not only for glucose but also for xylose release. The efficiencies of lactose decomposition and synthesis of galactooligosaccharides (GalOS) by CoGH1A were investigated at low (40 g L(-1)) and high (500 g L(-1)) initial lactose concentrations. At low lactose concentration, the time for decomposition of 83 % lactose was 10 min, which is much shorter than the reported 2-10 h for reaching such a decomposition rate. At high lactose concentration, after 50-min catalysis, the GalOS concentration reached 221 g L(-1) with a productivity of 265.2 g L(-1) h(-1). This productivity is at least 12-fold higher than those reported in literature.

CONCLUSIONS

The multifunctional glycoside hydrolase CoGH1A has high capabilities in saccharification of lignocellulosic biomass, decomposition of lactose, and synthesis of galactooligosaccharides. It is a promising enzyme to be used for bioconversion of carbohydrates in industrial scale. In addition, the results of this study indicate that the extremely thermophilic bacteria are potential resources for screening highly efficient glycoside hydrolases for the production of biofuels and biochemicals.

Two β-galactosidases from the human isolate Bifidobacterium breve DSM 20213: molecular cloning and expression, biochemical characterization and synthesis of galacto-oligosaccharides

Two β-galactosidases, β-gal I and β-gal II, from Bifidobacterium breve DSM 20213, which was isolated from the intestine of an infant, were overexpressed in Escherichia coli with co-expression of the chaperones GroEL/GroES, purified to electrophoretic homogeneity and biochemically characterized. Both β-gal I and β-gal II belong to glycoside hydrolase family 2 and are homodimers with native molecular masses of 220 and 211 kDa, respectively. The optimum pH and temperature for hydrolysis of the two substrates o-nitrophenyl-β-D-galactopyranoside (oNPG) and lactose were determined at pH 7.0 and 50°C for β-gal I, and at pH 6.5 and 55°C for β-gal II, respectively. The kcat/Km values for oNPG and lactose hydrolysis are 722 and 7.4 mM-1s-1 for β-gal I, and 543 and 25 mM-1s-1 for β-gal II. Both β-gal I and β-gal II are only moderately inhibited by their reaction products D-galactose and D-glucose. Both enzymes were found to be very well suited for the production of galacto-oligosaccharides with total GOS yields of 33% and 44% of total sugars obtained with β-gal I and β-gal II, respectively. The predominant transgalactosylation products are β-D-Galp-(1→6)-D-Glc (allolactose) and β-D-Galp-(1→3)-D-Lac, accounting together for more than 75% and 65% of the GOS formed by transgalactosylation by β-gal I and β-gal II, respectively, indicating that both enzymes have a propensity to synthesize β-(1→6) and β-(1→3)-linked GOS. The resulting GOS mixtures contained relatively high fractions of allolactose, which results from the fact that glucose is a far better acceptor for galactosyl transfer than galactose and lactose, and intramolecular transgalactosylation contributes significantly to the formation of this disaccharide.

Advances in research of intestinal lactase

DLactase is a type of disaccharidase which exists on the surface of small intestinal villi of mammals and can be generated by many beneficial intestinal bacteria. The majority of humans are deficient in lactase and approximately 2/3 of the world′s population are affected by lactase deficiency. Nowadays, the research of the metabolism of lactose, lactose enzyme expression and regulation has attracted wide attention both in China and other countries. In this article, we will review recent progresses in research of intestinal lactase.

Production of recombinant Bacillus subtilis chitosanase, suitable for biosynthesis of chitosan-oligosaccharides

Chitosanases are enzymes that catalyse the hydrolysis of the β-1,4 glycosidic bond of chitosan. One of the most promising applications of this enzyme is for the bioconversion of chitosan into value-added chitosan-oligosaccharides (COS). GH46 chitosanase (Csn) from Bacillus subtilis 168 was expressed in Escherichia coli by fusing the gene encoding mature Csn to the E. coli OmpA signal peptide sequence. The recombinant enzyme was secreted into the culture supernatant. The recombinant Csn showed high specific activity and stability over a wide range of pH. The enzyme was >100 times more thermostable in the presence of the substrate, with a half-life time of activity (τ(1/2)) of approximately 20 h at 50 °C and pH 5.5. Efficient bioconversion of chitosan into different mixtures of COS, using crude culture supernatant containing secreted enzyme was demonstrated.

The acid tolerant and cold-active β-galactosidase from Lactococcus lactis strain is an attractive biocatalyst for lactose hydrolysis

The gene encoding the β-galactosidase from the dairy Lactococcus lactis IL1403 strain was cloned, sequenced and overexpressed in Escherichia coli. The purified enzyme has a tetrameric arrangement composed of four identical 120 kDa subunits. Biochemical characterization showed that it is optimally active within a wide range of temperatures from 15 to 55 °C and of pH from 6.0 to 7.5. For its maximal activity this enzyme requires only 0.8 mM Fe(2+) and 1.6 mM Mg(2+). Purified protein displayed a high catalytic efficiency of 102 s(-1) mM(-1) for lactose. The enzyme stability was increased by immobilization mainly at low pH (from 4.0 to 5.5) and high temperatures (55 and 60 °C). The bioconversion of lactose using the L. lactis β-galactosidase allows the production of lactose with a high bioconversion rate (98 %) within a wide range of pH and temperature.