β-Galactosidase with transgalactosylation activity from Lactobacillus fermentum K4

Invited review: Properties of β-galactosidases derived from Lactobacillaceae species and their capacity for galacto-oligosaccharide production

β-galactosidase (enzymatic class 3.2.1.23) is one of the dairy industry's most important and widely used enzymes. The enzyme is part of a large family known to catalyze hydrolysis and transglycosylation reactions. Its hydrolytic activity is commonly used to decrease lactose content in dairy products, while its transglycosylase activity has recently been used to synthesize galacto-oligosaccharides (GOS). During the past couple of years, researchers have focused on studying β-galactosidase isolated and purified from lactic acid bacteria. This review will focus on β-galactosidase purified and characterized from what used to be the Lactobacillus genera. Furthermore, particular emphasis is given to its kinetics, biochemical characteristics, GOS production, market, and utilization by Lactobacilllaceae species.

In Vitro Production of Galactooligosaccharides by a Novel β-Galactosidase of Lactobacillus bulgaricus

β-galactosidase is an enzyme with dual activity and important industrial application. As a hydrolase, the enzyme eliminates lactose in milk, while as a trans-galactosidase it produces prebiotic galactooligosaccharides (GOS) with various degrees of polymerization (DP). The aim of the present study is the molecular characterization of β-galactosidase from a Bulgarian isolate, Lactobacillus delbrueckii subsp. bulgaricus 43. The sequencing of the β-gal gene showed that it encodes a new enzyme with 21 amino acid replacements compared to all other β-galactosidases of this species. The molecular model revealed that the new β-galactosidase acts as a tetramer. The amino acids D207, H386, N464, E465, Y510, E532, H535, W562, N593, and W980 form the catalytic center and interact with Mg²⁺ ions and substrate. The β-gal gene was cloned into a vector allowing heterologous expression of E. coli BL21(DE3) with high efficiency, as the crude enzyme reached 3015 U/mL of the culture or 2011 U/mg of protein. The enzyme's temperature optimum at 55 °C, a pH optimum of 6.5, and a positive influence of Mg²⁺, Mn²⁺, and Ca²⁺ on its activity were observed. From lactose, β-Gal produced a large amount of GOS with DP3 containing β-(1→3) and β-(1→4) linkages, as the latter bond is particularly atypical for the L. bulgaricus enzymes. DP3-GOS formation was positively affected by high lactose concentrations. The process of lactose conversion was rapid, with a 34% yield of DP3-GOS in 6 h, and complete degradation of 200 g/L of lactose for 12 h. On the other hand, the enzyme was quite stable at 55 °C and retained about 20% of its activity after 24 h of incubation at this temperature. These properties expand our horizons as regards the use of β-galactosidases in industrial processes for the production of lactose-free milk and GOS-enriched foods.

A review on enzyme-producing lactobacilli associated with the human digestive process: From metabolism to application

Complex carbohydrates, proteins, and other food components require a longer digestion process to be absorbed by the lining of the alimentary canal. In addition to the enzymes of the gastrointestinal tract, gut microbiota, comprising a large range of bacteria and fungi, has complementary action on the production of digestive enzymes. Within this universe of "hidden soldiers", lactobacilli are extensively studied because of their ability to produce lactase, proteases, peptidases, fructanases, amylases, bile salt hydrolases, phytases, and esterases. The administration of living lactobacilli cells has been shown to increase nutrient digestibility. However, it is still little known how these microbial-derived enzymes act in the human body. Enzyme secretion may be affected by variations in temperature, pH, and other extreme conditions faced by the bacterial cells in the human body. Besides, lactobacilli administration cannot itself be considered the only factor interfering with enzyme secretion, human diet (microbial substrate) being determinant in their metabolism. This review highlights the potential of lactobacilli to release functional enzymes associated with the digestive process and how this complex metabolism can be explored to contribute to the human diet. Enzymatic activity of lactobacilli is exerted in a strain-dependent manner, i.e., within the same lactobacilli species, there are different enzyme contents, leading to a large variety of enzymatic activities. Thus, we report current methods to select the most promising lactobacilli strains as sources of bioactive enzymes. Finally, a patent landscape and commercial products are described to provide the state of art of the transfer of knowledge from the scientific sphere to the industrial application.

Construction and Analysis of Food-Grade Lactobacillus kefiranofaciens β-Galactosidase Overexpression System

Lactobacillus kefiranofaciens contains two types of β-galactosidase, LacLM and LacZ, belonging to different glycoside hydrolase families. The difference in function between them has been unclear so far for practical application. In this study, LacLM and LacZ from L. kefiranofaciens ATCC51647 were cloned into constitutive lactobacillal expression vector pMG36e, respectively. Furtherly, pMG36n-lacs was constructed from pMG36e-lacs by replacing erythromycin with nisin as selective marker for food-grade expressing systems in Lactobacillus plantarum WCFS1, designated recombinant LacLM and LacZ respectively. The results from hydrolysis of o-nitrophenyl-β-galactopyranoside (ONPG) showed that the β-galactosidases activity of the recombinant LacLM and LacZ was 1460% and 670% higher than that of the original L. kefiranofaciens. Moreover, the lactose hydrolytic activity of recombinant LacLM was higher than that of LacZ in milk. Nevertheless, compare to LacZ, in 25% lactose solution the galacto-oligosaccharides (GOS) production of recombinant LacLM was lower. Therefore, two β-galactopyranosides could play different roles in carbohydrate metabolism of L. kefiranofaciens. In addition, the maximal growth rate of two recombinant strains were evaluated with different temperature level and nisin concentration in fermentation assay for practical purpose. The results displayed that 37°C and 20-40 U/ml nisin were the optimal fermentation conditions for the growth of recombinant β-galactosidase strains. Altogether the food-grade Expression system of recombinant β-galactosidase was feasible for applications in the food and dairy industry.

Optimal Production of β-Galactosidase from Lactobacillus fermentum for the Synthesis of Prebiotic Galactooligosaccharides (Gos)

The enzyme β-galactosidase (β-gal) has extensively used for improvement of lactose intolerance condition. Present study, was designed to assess the potential of β-gal enzyme produced by Lactobacillus fermentum, a kefir isolate, as a biocatalyst for the manufacture of prebiotic galactooligosaccharides (GOS) from lactose. The efficiency of L. fermentum to produce β-gal of 4,254 u/ml was determined by permeabilizing the cells with solvents such as sodium dodecyl sulfate (SDS) and chloroform. Different parameters contributing β-gal production including reaction time, temperature, pH, carbohydrates, and substrate concentration on L. fermentum were studied and optimum β-gal activity was found to be 6,232.13 u/ml. It was observed that different experimental parameters for pH (7.0), temperature (35°C), and carbohydrates (galactose) were statistically significant (p<0.05). L. fermentum was found to produce GOS by transgalactosylation catalysed by β-gal during lactose hydrolysis which yielded di, tri, and tetra oligosaccharides, confirmed by TLC and HPLC. The culture showed β-gal activity, suggesting biotechnological applications and a promising organism for industrial β-gal production.

Immobilization of β-Galactosidases on the Lactobacillus Cell Surface Using the Peptidoglycan-Binding Motif LysM

Lysin motif (LysM) domains are found in many bacterial peptidoglycan hydrolases. They can bind non-covalently to peptidoglycan and have been employed to display heterologous proteins on the bacterial cell surface. In this study, we aimed to use a single LysM domain derived from a putative extracellular transglycosylase Lp_3014 of Lactobacillus plantarum WCFS1 to display two different lactobacillal β-galactosidases, the heterodimeric LacLM-type from Lactobacillus reuteri and the homodimeric LacZ-type from Lactobacillus delbrueckii subsp. bulgaricus, on the cell surface of different Lactobacillus spp. The β-galactosidases were fused with the LysM domain and the fusion proteins, LysM-LacLMLreu and LysM-LacZLbul, were successfully expressed in Escherichia coli and subsequently displayed on the cell surface of L. plantarum WCFS1. β-Galactosidase activities obtained for L. plantarum displaying cells were 179 and 1153 U per g dry cell weight, or the amounts of active surface-anchored β-galactosidase were 0.99 and 4.61 mg per g dry cell weight for LysM-LacLMLreu and LysM-LacZLbul, respectively. LysM-LacZLbul was also displayed on the cell surface of other Lactobacillus spp. including L. delbrueckii subsp. bulgaricus, L. casei and L. helveticus, however L. plantarum is shown to be the best among Lactobacillus spp. tested for surface display of fusion LysM-LacZLbul, both with respect to the immobilization yield as well as the amount of active surface-anchored enzyme. The immobilized fusion LysM-β-galactosidases are catalytically efficient and can be reused for several repeated rounds of lactose conversion. This approach, with the β-galactosidases being displayed on the cell surface of non-genetically modified food-grade organisms, shows potential for applications of these immobilized enzymes in the synthesis of prebiotic galacto-oligosaccharides.

Multifunctional properties of Lactobacillus plantarum strains WiKim83 and WiKim87 as a starter culture for fermented food

This study aimed to evaluate the safety (hemolysis and enzyme activity), probiotic properties (gastrointestinal tract tolerance, adhesion, hydrophobicity, and auto-aggregation), and functional characteristics (antimicrobial, antioxidant, and β-galactosidase activities) of lactic acid bacteria (LAB), isolated from kimchi, in order to select a multifunctional LAB strain for starter culture in fermented food. The five isolated strains included Lactobacillus plantarum WiKim83, L. plantarum WiKim84, Pediococcus pentosaceus WiKim85, P. pentosaceus WiKim86, and L. plantarum WiKim87, as identified by 16S rRNA gene sequence analysis; they were confirmed to be nonhemolytic and not able to produce β-glucuronidase, a carcinogenic enzyme. Probiotic properties of the five LAB strains were evaluated relative to those of commercial Lactobacillus rhamnosus GG, and results revealed probiotic potential of three strains (L. plantarum WiKim83, L. plantarum WiKim84, and L. plantarum WiKim87) to be superior. L. plantarum WiKim84 showed high antimicrobial activity against pathogens, and L. plantarum WiKim83 exhibited the highest antioxidant and β-galactosidase activities. Based on the probiotic and functional properties, the main characteristics of each strain were highlighted and two of them, L. plantarum WiKim83 and L. plantarum WiKim87, were selected as the most potent by principal component analysis. These strains showed antimicrobial, β-galactosidase, and antioxidant activities, which recommend their suitability as starter culture in various fermented foods.

Beta galactosidases in Arabidopsis and tomato - a mini review

Beta galactosidases (BGALs) are glycosyl hydrolases that remove terminal β-D-galactosyl residues from β-D-galactosides. There are 17 predicted BGAL genes in the genomes of both Arabidopsis (BGAL1-17) and tomato (TBG1-17). All tested BGALs have BGAL activity but their distinct expression profiles and ancient phylogenetic separation indicates that these enzymes fulfil diverse, non-redundant roles in plant biology. The majority of these BGALs are predicted to have signal peptide and thought to act during cell wall-related biological processes. Interestingly, deletion of BGAL6 and BGAL10 in Arabidopsis causes reduced mucilage release during seed imbibition and shorter siliques respectively, whereas TBG4 depletion by RNAi decreases in fruit softening in tomato. The majority of plant BGALs remain to be characterized.

Engineering a thermostable Halothermothrix orenii β-glucosidase for improved galacto-oligosaccharide synthesis

Lactose is produced in large amounts as a by-product from the dairy industry. This inexpensive disaccharide can be converted to more useful value-added products such as galacto-oligosaccharides (GOSs) by transgalactosylation reactions with retaining β-galactosidases (BGALs) being normally used for this purpose. Hydrolysis is always competing with the transglycosylation reaction, and hence, the yields of GOSs can be too low for industrial use. We have reported that a β-glucosidase from Halothermothrix orenii (HoBGLA) shows promising characteristics for lactose conversion and GOS synthesis. Here, we engineered HoBGLA to investigate the possibility to further improve lactose conversion and GOS production. Five variants that targeted the glycone (-1) and aglycone (+1) subsites (N222F, N294T, F417S, F417Y, and Y296F) were designed and expressed. All variants show significantly impaired catalytic activity with cellobiose and lactose as substrates. Particularly, F417S is hydrolytically crippled with cellobiose as substrate with a 1000-fold decrease in apparent k cat, but to a lesser extent affected when catalyzing hydrolysis of lactose (47-fold lower k cat). This large selective effect on cellobiose hydrolysis is manifested as a change in substrate selectivity from cellobiose to lactose. The least affected variant is F417Y, which retains the capacity to hydrolyze both cellobiose and lactose with the same relative substrate selectivity as the wild type, but with ~10-fold lower turnover numbers. Thin-layer chromatography results show that this effect is accompanied by synthesis of a particular GOS product in higher yields by Y296F and F417S compared with the other variants, whereas the variant F417Y produces a higher yield of total GOSs.

Production and secretion of Lactobacillus crispatus β-galactosidase in Pichia pastoris

Lactobacillus β-galactosidases are mostly heterodimeric proteins, which are encoded by the two overlapping genes, lacL and lacM, and produced in recombinant prokaryotic systems for higher yield. This is the first report on the expression of a heterodimeric β-galactosidase from Lactobacillus crispatus B470 in Pichia pastoris. The overlapping consecutive genes, lacL and lacM, that shared 17 nucleotides were cloned from the genomic DNA of L. crispatus. A recombinant plasmid harboring both expression cassettes of lacL and lacM was constructed and transformed into P. pastoris GS115 competent cells. Two recombinant P. pastoris strains (GSLac01 and GSLac02) showed the highest β-galactosidase activities of 24.5 and 31.0 U/ml in the culture supernatants, respectively. The recombinant β-galactosidase (LcLacLM) from GSLac02 was purified to electrphoretic homogeneity by ion-exchange chromatography and molecular sieve chromatography. Similar to most Lactobacillus β-galactosidases that operate at moderately thermophilic and weak acid to neutral conditions, LcLacLM showed optimal activity at 50°C and pH 5.5-6.5. It's the first report on functional and secretory expression of LacLM-type β-galactosidase in eukaryotic system. This strategy might be applied to the expression of other overlapping genes.

β-galactosidase-catalyzed synthesis of galactosyl chlorphenesin and its characterization

We synthesized galactosyl chlorphenesin (CPN-G) using β-gal-containing Escherichia coli (E. coli) cells in which the conversion yield of chlorphenesin (CPN) to CPN-G reached about 64 % during 12 h. CPN-G was identified and characterized using high-performance liquid chromatography, liquid chromatography-mass spectrometry, Fourier transform-infrared spectrometry, and nuclear magnetic resonance analysis ((1)H and (13)C). We verified that a galactose was covalently bound to a CPN alcohol group during CPN-G synthesis throughout these analyses. In particular, by the hydrolysis of CPN-G using β-gal, it was confirmed that a galactose was bound to CPN. The minimal inhibitory concentration (MIC) results showed that the CPN-G MICs were fairly similar to those of CPN. HACAT cell viability was significantly higher in CPN-G-treated cells than in CPN-treated cells at concentrations of 0.0-20.0 mM. Finally, we accomplished the synthesis of less toxic CPN-G, compared with CPN, using β-gal-containing E. coli cells as whole cells without changes in the MICs against microorganisms.

MGcV: the microbial genomic context viewer for comparative genome analysis

Background

Conserved gene context is used in many types of comparative genome analyses. It is used to provide leads on gene function, to guide the discovery of regulatory sequences, but also to aid in the reconstruction of metabolic networks. We present the Microbial Genomic context Viewer (MGcV), an interactive, web-based application tailored to strengthen the practice of manual comparative genome context analysis for bacteria.

Results

MGcV is a versatile, easy-to-use tool that renders a visualization of the genomic context of any set of selected genes, genes within a phylogenetic tree, genomic segments, or regulatory elements. It is tailored to facilitate laborious tasks such as the interactive annotation of gene function, the discovery of regulatory elements, or the sequence-based reconstruction of gene regulatory networks. We illustrate that MGcV can be used in gene function annotation by visually integrating information on prokaryotic genes, like their annotation as available from NCBI with other annotation data such as Pfam domains, sub-cellular location predictions and gene-sequence characteristics such as GC content. We also illustrate the usefulness of the interactive features that allow the graphical selection of genes to facilitate data gathering (e.g. upstream regions, ID’s or annotation), in the analysis and reconstruction of transcription regulation. Moreover, putative regulatory elements and their corresponding scores or data from RNA-seq and microarray experiments can be uploaded, visualized and interpreted in (ranked-) comparative context maps. The ranked maps allow the interpretation of predicted regulatory elements and experimental data in light of each other.

Conclusion

MGcV advances the manual comparative analysis of genes and regulatory elements by providing fast and flexible integration of gene related data combined with straightforward data retrieval. MGcV is available at http://mgcv.cmbi.ru.nl.