Exploring the acidotolerance of beta-galactosidase from Lactobacillus delbrueckii subsp. bulgaricus: an attractive enzyme for lactose bioconversion

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.

Crosstalk Between Intestinal Microbiota Derived Metabolites and Tissues in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an evidence based- cellular immunotherapy for hematological malignancies. Immune reactions not only promote graft-versus-tumor effects that kill hematological malignant cells but also graft-versus-host disease (GVHD) that is the primary complication characterized by systemic organ damages consisting of T-cells and antigen presenting cells (APCs) activation. GVHD has long been recognized as an immunological reaction that requires an immunosuppressive treatment targeting immune cells. However immune suppression cannot always prevent GVHD or effectively treat it once it has developed. Recent studies using high-throughput sequencing technology investigated the impact of microbial flora on GVHD and provided profound insights of the mechanism of GVHD other than immune cells. Allo-HSCT affects the intestinal microbiota and microbiome-metabolome axis that can alter intestinal homeostasis and the severity of experimental GVHD. This axis can potentially be manipulated via dietary intervention or metabolites produced by intestinal bacteria affected post-allo-HSCT. In this review, we discuss the mechanism of experimental GVHD regulation by the complex microbial community-metabolites-host tissue axis. Furthermore, we summarize the major findings of microbiome-based immunotherapeutic approaches that protect tissues from experimental GVHD. Understanding the complex relationships between gut microbiota-metabolites-host tissues axis provides crucial insight into the pathogenesis of GVHD and advances the development of new therapeutic approaches.

Antarctic Rahnella inusitata: A Producer of Cold-Stable β-Galactosidase Enzymes

There has been a recent increase in the exploration of cold-active β-galactosidases, as it offers new alternatives for the dairy industry, mainly in response to the current needs of lactose-intolerant consumers. Since extremophilic microbial compounds might have unique physical and chemical properties, this research aimed to study the capacity of Antarctic bacterial strains to produce cold-active β-galactosidases. A screening revealed 81 out of 304 strains with β-galactosidase activity. The strain Se8.10.12 showed the highest enzymatic activity. Morphological, biochemical, and molecular characterization based on whole-genome sequencing confirmed it as the first Rahnella inusitata isolate from the Antarctic, which retained 41–62% of its β-galactosidase activity in the cold (4 °C–15 °C). Three β-galactosidases genes were found in the R. inusitata genome, which belong to the glycoside hydrolase families GH2 (LacZ and EbgA) and GH42 (BglY). Based on molecular docking, some of these enzymes exhibited higher lactose predicted affinity than the commercial control enzyme from Aspergillus oryzae. Hence, this work reports a new Rahnella inusitata strain from the Antarctic continent as a prominent cold-active β-galactosidase producer.

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.

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.

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.

Production Optimization of an Active β-Galactosidase of Bifidobacterium animalis in Heterologous Expression Systems

β-Galactosidase (E.C.3.2.1.23) catalyzes the hydrolysis of lactose into glucose and galactose and the synthesis of galacto-oligosaccharides as well. The β-galactosidases from bacteria, especially lactobacilli, and yeast have neutral pH and are much more likely to be developed as food additives. However, the challenges of cumbersome purification, product toxicity, and low yield in protein production have limited the commercialization of many excellent candidates. In this study, we identified a β-galactosidase gene (bg42-106) in Bifidobacterium animalis ACCC05790 and expressed the gene product in Escherichia coli BL21(DE3) and Pichia pastoris GS115, respectively. The recombinant bG42-106 purified from E. coli cells was found to be optimally active at pH 6.0 and 60°C and had excellent stability over a wide pH range (5.0–8.0) and at high temperature (60°C). The specific activity of bG42-106 reached up to 2351 U/mg under optimal conditions. The galacto-oligosaccharide yield was 24.45 g/L after incubation with bG42-106 at 60°C for 2 h. When recombinant bG42-106 was expressed in Pichia pastoris GS115, it was found in the culture medium but only at a concentration of 1.73 U/ml. To increase its production, three strategies were employed, including codon optimization, disulfide formation, and fusion with a Cherry tag, with Cherry-tag fusion being most effective. The culture medium of P. pastoris that expressed Cherry-tagged bG42-106 contained 24.4 U/mL of β-galactosidase activity, which is 14-fold greater than that produced by culture of P. pastoris harboring wild-type bG42-106.

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.

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.

The sensitivity and significance analysis of parameters in the model of pH regulation on lactic acid production by Lactobacillus bulgaricus

Background

The excessive production of lactic acid by L. bulgaricus during yogurt storage is a phenomenon we are always tried to prevent. The methods used in industry either control the post-acidification inefficiently or kill the probiotics in yogurt. Genetic methods of changing the activity of one enzyme related to lactic acid metabolism make the bacteria short of energy to growth, although they are efficient ways in controlling lactic acid production.

Results

A model of pH-induced promoter regulation on the production of lactic acid by L. bulgaricus was built. The modelled lactic acid metabolism without pH-induced promoter regulation fitted well with wild type L. bulgaricus (R²_LAC = 0.943, R²_LA = 0.942). Both the local sensitivity analysis and Sobol sensitivity analysis indicated parameters T_max, GR, K_LR, S, V₀, V₁ and d_LR were sensitive. In order to guide the future biology experiments, three adjustable parameters, K_LR, V₀ and V₁, were chosen for further simulations. V₀ had little effect on lactic acid production if the pH-induced promoter could be well induced when pH decreased to its threshold. K_LR and V₁ both exhibited great influence on the producing of lactic acid.

Conclusions

The proposed method of introducing a pH-induced promoter to regulate a repressor gene could restrain the synthesis of lactic acid if an appropriate strength of promoter and/or an appropriate strength of ribosome binding sequence (RBS) in lacR gene has been designed.

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.

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.

Characterization of a heterodimeric GH2 β-galactosidase from Lactobacillus sakei Lb790 and formation of prebiotic galacto-oligosaccharides

The lacLM genes from Lactobacillus sakei Lb790, encoding a heterodimeric β-galactosidase that belongs to glycoside hydrolase family GH2, were cloned and heterologously expressed in Escherichia coli . Subsequently, the recombinant β-galactosidase LacLM was purified to apparent homogeneity and characterized. The enzyme is a β-galactosidase with narrow substrate specificity because o-nitrophenyl-β-D-galactopyranoside (oNPG) was efficiently hydrolyzed, whereas various structurally related oNP analogues were not. The K(m) and k(cat) values for oNPG and lactose were 0.6 mM and 180 s(-1) and 20 mM and 43 s(-1), respectively. The enzyme is inhibited competitively by its two end-products D-galactose and D-glucose (K(i) values of 180 and 475 mM, respectively). As judged by the ratio of the inhibition constant to the Michaelis constant, K(i)/K(m), this inhibition is only very moderate and much less pronounced than for other microbial β-galactosidases. β-Galactosidase from L. sakei possesses high transgalactosylation activity and was used for the synthesis of galacto-oligosaccharides (GalOS), employing lactose at a concentration of 215 g/L. The maximum GalOS yield was 41% (w/w) of total sugars at 77% lactose conversion and contained mainly non-lactose disaccharides, trisaccharides, and tetrasaccharides with approximately 38, 57, and 5% of total GalOS formed, respectively. The enzyme showed a strong preference for the formation of β-(1→6)-linked transgalactosylation products, whereas β-(1→3)-linked compounds were formed to a lesser extent and β-(1→4)-linked reaction products could not be detected.

Efficient bioconversion of lactose in milk and whey: immobilization and biochemical characterization of a beta-galactosidase from the dairy Streptococcus thermophilus LMD9 strain

The gene encoding beta-galactosidase from dairy Streptococcus thermophilus strain LMD9 was cloned, sequenced and expressed in Escherichia coli. The recombinant enzyme was purified and showed high specific activity of 464 U/mg. This protein displays a homotetrameric arrangement composed of four 118 kDa monomers. Monitoring of the activity showed that this enzyme was optimally active at a wide range of temperatures (25-40 degrees C) and at pH from 6.5 to 7.5. Immobilization of the recombinant E. coli in alginate beads clearly enhanced the enzyme activity at various temperatures, including 4 and 50 degrees C, and at pH values from 4.0 to 8.5. Stability studies indicated that this biocatalyst has high stability within a broad range of temperatures and pH. This stability was improved not only by addition of 1 mM of Mn(2+) and 1.2 mM Mg(2+), but essentially through immobilization. The remarkable bioconversion rates of lactose in milk and whey at different temperatures revealed the attractive catalytic efficiency of this enzyme, thus promoting its use for lactose hydrolysis in milk and other dairy products.