Comparison of three tannases cloned from closely related lactobacillus species: L. Plantarum, L. Paraplantarum, and L. Pentosus

Food phenolics and Lactiplantibacillus plantarum

Phenolic compounds are important constituents of plant food products. These compounds play a key role in food characteristics such as flavor, astringency and color. Lactic acid bacteria are naturally found in raw vegetables, being Lactiplantibacillus plantarum the most commonly used commercial starter for the fermentation of plant foods. Hence, the metabolism of phenolic compounds of L. plantarum has been a subject of study in recent decades. Such studies confirm that L. plantarum, in addition to presenting catalytic capacity to transform aromatic alcohols and phenolic glycosides, exhibits two main differentiated metabolic routes that allow the biotransformation of dietary hydroxybenzoic and hydroxycinnamic acid-derived compounds. These metabolic pathways lead to the production of new compounds with new biological and organoleptic properties. The described metabolic pathways involve the action of specialized esterases, decarboxylases and reductases that have been identified through genetic analysis and biochemically characterized. The purpose of this review is to provide a comprehensive and up-to-date summary of the current knowledge of the metabolism of food phenolics in L. plantarum.

Gut microbiota metabolites, redox status, and the related regulatory effects of probiotics

Oxidative stress is a state of imbalance between oxidation and antioxidation. It is caused by excess levels of free radicals and leads to the damage of DNA, proteins, and lipids. The crucial role of gut microbiota in regulating oxidative stress has been widely demonstrated. Studies have suggested that the redox regulatory effects of gut microbiota are related to gut microbiota metabolites, including fatty acids, lipopolysaccharides, tryptophan metabolites, trimethylamine-N-oxide and polyphenolic metabolites. In recent years, the potential benefits of probiotics have been gaining increasing scientific interest owing to their ability to modulate gut microbiota and oxidative stress. In this review, we summarise the adverse health effects of oxidative stress and discuss the role of the gut microbiota and its metabolites in redox regulation. Based on the influence of gut microbiota metabolites, the roles of probiotics in preventing oxidative stress are highlighted.

Selection of Lactiplantibacillus Strains for the Production of Fermented Table Olives

Lactiplantibacillus strains (n. 77) were screened for technological properties (e.g., xylose fermentation, EPS production, antimicrobial activity, tolerance to NaCl and phenolic compounds, oleuropein degradation and hydroxytyrosol formation) relevant for the production of fermented table olives. Survival to olive mill wastewater (OMW) and to simulated gastro-intestinal tract (GIT), the capability to grow at different combinations of NaCl and pH values, radical scavenging activities and biofilm formation were further investigated in 15 selected strains. The screening step revealed high diversity among Lactiplantibacillus strains. Most of the strains were able to ferment xylose, while only a few strains produced EPS and had inhibitory activity against Y. lipolytica. Resistance to phenolic compounds (gallic, protocatechuic, hydroxybenzoic and syringic acids), as well as the ability to release hydroxytyrosol from oleuropein, was strain-specific. OMWs impaired the survival of selected strains, while combinations of NaCl ≤ 6% and pH ≥ 4.0 were well tolerated. DPPH and hydroxyl radical degradation were strain-dependent, while the capability to form biofilm was affected by incubation time. Strains were very tolerant to the GIT. The genome of Lpb. pentosus O17 was sequenced and analysed to verify the presence of genes involved in the degradation and metabolism of phenolic compounds. O17 lacks carboxylesterase and gallate decarboxylase (subunits B and D) sequences, and its gene profile differs from that of other publicly available Lpb. pentosus genomes.

Improving the Acid Resistance of Tannase TanBLp (AB379685) from Lactobacillus plantarum ATCC14917T by Site-Specific Mutagenesis

Tannin acyl hydrolase referred commonly as tannase catalyzes the hydrolysis of the galloyl ester bond of tannin to release gallic acid. The tannase TanBLp which cloned from Lactobacillus plantarum ATCC14917^T has high activity in the pH range (7.0-9.0) at 40 °C, it would be detrimental to the utilization at acidic environment. The catalytic sites and stability of TanBLp were analyzed using bioinformatics and site-specific mutagenesis. The results reiterated that the amino acid residues Ala164, Lys343, Glu357, Asp421 and His451 had played an important role in maintaining the activity. The optimum pH of mutants V75A, G77A, N94A, A164S and F243A were shifted from 8.0 to 6.0, and mutant V75A has the highest pH stability and activity at acidic conditions than other mutants, which was more suitable for industrial application to manufacture gallic acid. This study was of great significance to promote the industrialization and efficient utilization of tannase TanBLp.

Structural diversity and substrate preferences of three tannase enzymes encoded by the anaerobic bacterium Clostridium butyricum

Tannins are secondary metabolites that are enriched in the bark, roots, and knots in trees and are known to hinder microbial attack. The biological degradation of water-soluble gallotannins, such as tannic acid, is initiated by tannase enzymes (EC 3.1.1.20), which are esterases able to liberate gallic acid from aromatic-sugar complexes. However, only few tannases have previously been studied in detail. Here, for the first time, we biochemically and structurally characterize three tannases from a single organism, the anaerobic bacterium Clostridium butyricum, which inhabits both soil and gut environments. The enzymes were named CbTan1-3, and we show that each one exhibits a unique substrate preference on a range of galloyl ester model substrates; CbTan1 and 3 demonstrated preference toward galloyl esters linked to glucose, while CbTan2 was more promiscuous. All enzymes were also active on oak bark extractives. Furthermore, we solved the crystal structure of CbTan2 and produced homology models for CbTan1 and 3. In each structure, the catalytic triad and gallate-binding regions in the core domain were found in very similar positions in the active site compared with other bacterial tannases, suggesting a similar mechanism of action among these enzymes, though large inserts in each enzyme showcase overall structural diversity. In conclusion, the varied structural features and substrate specificities of the C. butyricum tannases indicate that they have different biological roles and could further be used in development of new valorization strategies for renewable plant biomass.

Degradation of epigallocatechin and epicatechin gallates by a novel tannase TanHcw from Herbaspirillum camelliae

Background

Herbaspirillum camelliae is a gram-negative endophyte isolated from the tea plant. Both strains WT00C and WT00F were found to hydrolyze epigallocatechin-3-gallate (EGCG) and epicatechin-3-gallate (ECG) to release gallic acid (GA) and display tannase activity. However, no tannase gene was annotated in the genome of H. camelliae WT00C.

Results

The 39 kDa protein, annotated as the prolyl oligopeptidase in the NCBI database, was finally identified as a novel tannase. Its gene was cloned, and the enzyme was expressed in E. coli and purified to homogeneity. Moreover, enzymatic characterizations of this novel tannase named Tan_Hcw were studied. Tan_Hcw was a secretary enzyme with a Sec/SPI signal peptide of 48 amino acids at the N-terminus, and it catalyzed the degradation of tannin, methyl gallate (MG), epigallocatechin-3-gallate (EGCG) and epicatechin-3-gallate (ECG). The optimal temperature and pH of Tan_Hcw activities were 30 °C, pH 6.0 for MG and 40 °C, pH 7.0 for both EGCG and ECG. Na⁺, K⁺ Mn²⁺ and Triton-X100, Tween80 increased the enzyme activity of Tan_Hcw, whereas Zn²⁺, Mg²⁺, Hg²⁺, EMSO, EDTA and β-mercaptoethanol inhibited enzyme activity. K_m, k_cat and k_cat /K_m of Tan_Hcw were 0.30 mM, 37.84 s⁻¹, 130.67 mM⁻¹ s⁻¹ for EGCG, 0.33 mM, 34.59 s⁻¹, 105.01 mM⁻¹ s⁻¹ for ECG and 0.82 mM, 14.64 s⁻¹, 18.17 mM⁻¹ s⁻¹ for MG, respectively.

Conclusion

A novel tannase Tan_Hcw from H. camelliae has been identified and characterized. The biological properties of Tan_Hcw suggest that it plays a crucial role in the specific colonization of H. camelliae in tea plants. Discovery of the tannase Tan_Hcw in this study gives us a reasonable explanation for the host specificity of H. camelliae. In addition, studying the characteristics of this enzyme offers the possibility of further defining its potential in industrial application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01685-1.

Acid Stable Yeast Cell-Associated Tannase with High Capability in Gallated Catechin Biotransformation

Previously, nine tannin-tolerant and tannase-producing yeasts were isolated from Miang; all produced cell-associated tannase (CAT) during growth in tannin substrate. Among which, only CAT from Sporidiobolus ruineniae showed better stability than its purified form. Yet, it is of particular interest to directly characterize CATs from the latter yeasts. In this study, four CATs from yeasts, namely Cyberlindnera rhodanensis A22.3, Candida sp. A39.3, Debaryomyces hansenii A45.1, and Cy. rhodanensis A45.3 were characterized. The results indicate that all CATs were produced within the same production yield (11 mU/mL). Most CATs exhibited similar pH and temperature optima and stabilities, except for CAT from Cy. rhodanensis A22.3. This CAT was assigned as acid-stable tannase due to its unusual optimum pH of 2.0 with pH stability and half-life thermostability in the range of pH 2.0-4.0, and 70 °C, respectively. All CATs demonstrated high substrate specificity toward epigallocatechin gallate and epicatechin gallate, thus forming epigallocatechin and epicatechin, respectively. Moreover, they showed operational stability to repeated use for up to five cycles without loss of the initial activity. Therefore, CATs from these yeasts could be useful for the extraction and biotransformation of tea catechins and related applications.

Role of dietary polyphenols on gut microbiota, their metabolites and health benefits

The beneficial health roles of dietary polyphenols in preventing oxidative stress related chronic diseases have been subjected to intense investigation over the last two decades. As our understanding of the role of gut microbiota advances our knowledge of the antioxidant and anti-inflammatory functions of polyphenols accumulates, there emerges a need to examine the prebiotic role of dietary polyphenols. This review focused onthe role of different types and sources of dietary polyphenols on the modulation of the gut microbiota, their metabolites and how they impact on host health benefits. Inter-dependence between the gut microbiota and polyphenol metabolites and the vital balance between the two in maintaining the host gut homeostasis were discussed with reference to different types and sources of dietary polyphenols. Similarly, the mechanisms behind the health benefits by various polyphenolic metabolites bio-transformed by gut microbiota were also explained. However, further research should focus on the importance of human trials and profound links of polyphenols-gut microbiota-nerve-brain as they provide the key to unlock the mechanisms behind the observed benefits of dietary polyphenols found in vitro and in vivo studies.

Contributions of protein microenvironment in tannase industrial applicability: An in-silico comparative study of pathogenic and non-pathogenic bacterial tannase

Tannase is an inducible industrially important enzyme, produced by several microorganisms. A large number of bacteria have reported as tannase producers; however, some of them are pathogenic in nature. Therefore, it is quite uncertain whether the application of these tannase enzymes from such pathogenic bacteria is suitable for industries and human welfare. Till date, there is no clear evidence regarding which group of bacteria (non-pathogenic or pathogenic) is better suited for their application in the edge of industries with particular reference to the food industry. The present study is following the findings of the above queries. In this study, a large number of tannase protein sequences have been retrieved from the databases, including both non-pathogenic and pathogenic bacterial species. Physiochemical and evolutionary properties of those sequences have been evaluated. Results have shown that non-pathogenic bacterial tannase possesses a high number of acidic and basic amino acid residues as compared to their pathogenic counterparts. The acidic and basic amino acid residues of tannase provide unique microenvironment to it. In the other hand, the numbers of disorder forming residues are higher in tannase sequences of pathogenic bacteria. The study of tannase microenvironment leads in the formation of salt bridges, which finally favoring the stability and proper functioning of tannase. This is the first report of such observation on tannase enzyme using in silico approach. Study of the microenvironment concept will be helpful in protein engineering.

Changes in lactic acid bacteria and components of Awa-bancha by anaerobic fermentation

Awa-bancha is a post-fermented tea produced in Naka and Kamikatsu, Tokushima, Japan. We investigated the lactic acid bacteria in each stage of production of Awa-bancha and evaluated the relationships with the components. Lactic acid bacteria were isolated from tea leaves cultured with de Man, Rogosa, and Sharpe (MRS) agar plates, and the species were identified by homology of the 16 S rRNA gene and multiplex polymerase chain reaction (PCR) of the recA gene to distinguish the Lactobacillus plantarum group. As a result, a variety of species were isolated from the raw tea leaves, and Lactobacillus pentosus was isolated most frequently after anaerobic fermentation. Regarding the tea leaf components, organic acids, such as lactic acid, increased, free amino acids decreased, and catechins changed owing to anaerobic fermentation. Our results suggest that the microbial flora mainly composed of L. pentosus is important in the anaerobic fermentation process for flavor formation of Awa-bancha.

Expression and biochemical characterization of a new alkaline tannase from Lactobacillus pentosus

Lactobacillus pentosus BA-7 and L. pentosus QA1-5 are tannin-tolerant lactic acid bacteria that were isolated from Miang, a traditional fermented tea-leaf found in northern Thailand and a tannin-rich substrate. Tannase encoding genes were isolated, cloned and overexpressed in Escherichia coli BL21(DE3). The recombinant tannase was produced with production yields of 40 and 39 KU/L for LpTanBA-7 and LpTanQA1-5, respectively. Both revealed the same molecular weight of 50 kDa as estimated by SDS-PAGE and were optimally active under alkaline pH conditions LpTanQA1-5 revealed optimal temperatures in a range of 37-40 °C as is typically found in lactic acid bacteria, while LpTanBA-7 was active at higher temperatures with an optimum temperature range of 45-55 °C. LpTanBA-7 was found to be more stable within the same range of temperatures than LpTanQA1-5. Furthermore, it was active and stable toward various organic solvents and produced 50 mg/mL of gallic acid from 100 mg/mL tannic acid. Based on the results, LpTanBA-7 is considered a new alkali-moderately thermophilic tannase obtained from lactic acid bacterium that may be capable of a feasible production capacity of gallic acid and its esters. Furthermore, tannase that is active at high temperatures could also be used in tea products in order to develop a sweet aftertaste, as well as to improve levels of antioxidant activity.

Bacterial tannases: classification and biochemical properties

Tannin acyl hydrolases, also known as tannases, are a group of enzymes critical for the transformation of tannins. The study of these enzymes, which initially evolved in different organisms to detoxify and/or use these plant metabolites, has nowadays become relevant in microbial enzymology research due to their relevant role in food tannin transformation. Microorganisms, particularly bacteria, are major sources of tannase. Cloning and heterologous expression of bacterial tannase genes and structural studies have been performed in the last few years. However, a systematic compilation of the information related to all recombinant tannases, their classification, and characteristics is missing. In this review, we explore the diversity of heterologously produced bacterial tannases, describing their substrate specificity and biochemical characterization. Moreover, a new classification based on sequence similarity analysis is proposed. Finally, putative tannases have been identified in silico for each group of tannases taking advantage of the use of the "tannase" distinctive features previously proposed.

Potential Prebiotic Properties of Nuts and Edible Seeds and Their Relationship to Obesity

Obesity is a global epidemic chronic condition and is progressing at a rapid rate. This review focuses on the potential prebiotic properties of nuts and edible seeds and the plausible mechanisms that their consumption may help the prevention and the management of overweight and obesity. The literature review was performed by searching papers about the topic in MEDLINE and SCOPUS databases. The healthy attributes of nuts and edible seeds, especially dietary fibers and polyphenols contents, indicate that their mechanism of weight gain prevention may occur through interaction with the gut microbiota, by means of prebiotic effects. Among the etiological factors associated with obesity, the gut microbiota seems to play a significant role. Dysbiosis causes an imbalance in energy homeostasis that contributes to obesity. Three mechanisms are proposed in this review to explain the potential role of nut and edible seed consumption on intestinal homeostasis and body weight control: maintenance of the enteric barrier integrity, improvement of anti-inflammatory status and enhancement of butyrate synthesis. Further high-quality clinical trials should explore the interaction between oilseed consumption, microbiota, and body adiposity control, particularly investigating the microbiota metabolites and their relation to the prevention and management of obesity.

Expression of Aspergillus niger N5-5 in E. coli and purification and identification of products

Due to the feature of high hydrolysis, tannase is widely used in food, beverage, brewing and other fields. However, high cost in producing natural tannase makes it difficult to apply tannase to industry in a large-scale. Microbial expression systems can be used for preparing numerous amount of enzyme at low cost, so in this paper Aspergillus niger N5-5 was expressed using E. coli system. Specific primers were designed based on the Aspergillus niger N5-5 sequence N3 (GenBank, No.: KP677552), and tannase gene tan was promoted to carry 6 His tag and enzyme cutting site which contains NdeI/HindIII using PCR amplification. Then, tannase gene tan was connected to expression vector by NdeI/HindIII enzyme cutting. In this way, recombinant expression vector tan-pET43.1a was formed. Then, the expression vector pET43.1a by NdeI/HindIII enzyme cutting was transformed into E. coli BL21 (DE3) to induce expression of Aspergillus niger N5-5. When the induced fungi were disrupted by the ultrasonic wave, the crude enzyme was extracted and purified by using the IMAC, and then the activity of the crude enzyme and pure enzyme was determined. According to the results of determination of the tannase activity, the tannase activity of the crude enzyme was greatly improved after the crude enzyme was purified, and the specific activity of the pure enzyme was about 8 times of that of the crude enzyme. The results of SDS-PAGE of the pure enzyme showed that the molecular mass of the pure enzyme was about 65 kDa/64–65 kDa, which was consistent with the expected result (64.2 kDa), It can be concluded that the crude enzyme solution was purified successfully. The results of pure enzyme’s protein identification by Western Blotting showed that clear protein bands pro-3 were observed. Molecular mass of clear protein bands pro-3 was about 65 kDa, which was in line with the expected results (64.2 kDa). It can be seen that the aforementioned expression protein could be specifically combined with His tag. It proved expression protein to be a recombinant fusion protein with 6 His tag.

Diversity of lactic acid bacteria from Miang, a traditional fermented tea leaf in northern Thailand and their tannin-tolerant ability in tea extract

The microbiota of lactic acid bacteria (LAB) in thirty-five samples of Miang, a traditional fermented tea leaf product, collected from twenty-two different regions of eight provinces in upper northern Thailand was revealed through the culture-dependent technique. A total of 311 presumptive LAB strains were isolated and subjected to clustering analysis based on repetitive genomic element-PCR (rep-PCR) fingerprinting profiles. The majority of the strains belonged to the Lactobacillus genera with an overwhelming predominance of the Lb. plantarum group. Further studies of species-specific PCR showed that 201 of 252 isolates in the Lb. plantarum group were Lb. plantarum which were thus considered as the predominant LAB in Miang, while the other 51 isolates belonged to Lb. pentosus. In contrast to Lb. plantarum, there is a lack of information on the tannase gene and the tea tannin-tolerant ability of Lb. pentosus. Of the 51 Lb. pentosus isolates, 33 were found to harbor the genes encoding tannase and shared 93-99% amino acid identity with tannase obtained from Lb. pentosus ATCC 8041^T. Among 33 tannase gene-positive isolates, 23 isolates exhibited high tannin- tolerant capabilities when cultivated on de Man Rogosa and Sharpe agar-containing bromocresol purple (0.02 g/L, MRS-BCP) supplemented with 20% (v/v) crude tea extract, which corresponded to 2.5% (w/v) tannins. These Lb. pentosus isolates with high tannin-tolerant capacity are expected to be the high potential strains for functional tannase production involved in Miang fermentation as they will bring about certain benefits and could be used to improve the fermentation of tea products.

Characterization of Feruloyl Esterases Produced by the Four Lactobacillus Species: L. amylovorus, L. acidophilus, L. farciminis and L. fermentum, Isolated from Ensiled Corn Stover

Lactic acid bacteria (LAB) play important roles in silage fermentation, which depends on the production of sufficient organic acids to inhibit the growth of undesirable microorganisms. However, LAB are not able to degrade cellulose and hemicellulose. Bacteria and fibrolytic enzymes are usually used as inoculants to improve the silage quality and digestibility. In the present study, we isolated four Lactobacillus strains (L. amylovorus CGMCC 11056, L. acidophilus CCTCC AB2010208, L. farciminis CCTCC AB2016237 and L. fermentum CCTCC AB2010204) with feruloyl esterase (FAE) activities from ensiled corn stover (CS) by a plate screening assay. The genes encoding FAEs were cloned and hetero-expressed in Escherichia coli. The optimal temperature and pH of these purified enzymes ranged from 45 to 50°C and from 7.0 to 8.0, respectively. They could hydrolyze hydroxycinnamoyl esters in a substrate-specific manner when methyl ferulate, methyl caffeate, methyl ρ-coumarate and methyl sinapinate were used as substrates. Moreover, these four FAEs were able to hydrolyze CS to release hydroxycinnamic acids. Furthermore, these strains could degrade hydroxycinnamic esters, and L. amylovorus CGMCC 11056 was the most efficient strain among these four isolates. These results provided a new target for the development of inoculants to improve silage quality and digestibility.

Expression, purification and immobilization of tannase from Staphylococcus lugdunensis MTCC 3614

Enzymes find their applications in various industries, due to their error free conversion of substrate into product. Tannase is an enzyme used by various industries for degradation of tannin. Biochemical characterization of a specific enzyme from one organism to other is one of the ways to search for enzymes with better traits for industrial applications. Here, tannase encoding gene from Staphylococcus lugdunensis was cloned and suitability of the enzyme in various conditions was analysed to find its application in various industry. The recombinant protein was expressed with 6× His tag and purified using nickel affinity beads. The enzyme was purified up to homogeneity, with approximate molecular weight of 66 kDa. Purified tannase exhibited specific activity of about 716 U/mg. Optimum enzyme activity was found to be 40 °C at pH 7.0. Biochemical characterization revealed; metal ions such as Zn2+, Fe2+, Fe3+ and Mn2+ inhibited tannase activity, and SDS at lower concentration, increased tannase activity. Non polar organic solvents increased the tannase activity and polar solvents inhibited the tannase activity. Tannase immobilization studies show protection of the enzyme under wide range of pH and temperature. Also in this study we report a method for recovery and repeated use of the tannase.

Nucleotide and amino acid variations of tannase gene from different Aspergillus strains

Tannase is an enzyme that catalyses the hydrolysis of ester bonds present in tannins. Most of the scientific reports about this biocatalysis focus on aspects related to tannase production and its recovery; on the other hand, reports assessing the molecular aspects of the tannase gene or protein are scarce. In the present study, a tannase gene fragment from several Aspergillus strains isolated from the Mexican semidesert was sequenced and compared with tannase amino acid sequences reported in NCBI database using bioinformatics tools. The genetic relationship among the different tannase sequences was also determined. A conserved region of 7 amino acids was found with the conserved motif GXSXG common to esterases, in which the active-site serine residue is located. In addition, in Aspergillus niger strains GH1 and PSH, we found an extra codon in the tannase sequences encoding glycine. The tannase gene belonging to semidesert fungal strains followed a neutral evolution path with the formation of 10 haplotypes, of which A. niger GH1 and PSH haplotypes are the oldest.