Cohnella amylopullulanases: Biochemical characterization of two recombinant thermophilic enzymes

Pullulanase: unleashing the power of enzyme with a promising future in the food industry

Pullulanases are the most important industrial group of enzymes in family 13 glycosyl hydrolases. They hydrolyze either α-1,6 and α-1,4 or both glycosidic bonds in pullulan as well as other carbohydrates to produce glucose, maltose, and maltotriose syrups, which have important uses in food and other related sectors. However, very less reports are available on pullulanase production from native strains because of low yield issues. In line with the increasing demands for pullulanase, it has become important to search for novel pullulanase-producing microorganisms with high yields. Moreover, high production costs and low yield are major limitations in the industrial production of pullulanase enzymes. The production cost of pullulanase by using the solid-state fermentation (SSF) process can be minimized by selecting agro-industrial waste. This review summarizes the types, sources, production strategies, and potential applications of pullulanase in different food and other related industries. Researchers should focus on fungal strains producing pullulanase for better yield and low production costs by using agro-waste. It will prove a better enzyme in different food processing industries and will surely reduce the cost of products.

Properties of a neutral, thermally stable and surfactant-tolerant pullulanase from worker termite gut-dwelling Bacillus safensis as potential for industrial applications

The gut of termite has been observed to host communities of bacteria which exhibited pullulan-degrading ability. Bacillus safensis displayed maximum pullulanase (a debranching enzyme) activity and it was therefore selected for production, purification and characterization of pullulanase which was the aim of the study. The crude enzyme obtained from the pullulanase production medium was subjected to ammonium sulphate precipitation, ion exchange and gel-filtration chromatography and the physicochemical properties of the purified was thereafter characterized. A purified pullulanase with the yield of 13% and 24-fold purification was obtained and its homogeneity was established by molecular weight of 42 kDa. The optimum pH 7 and 60 °C were obtained while the enzyme was stable between 40-60 °C and pH 4–5 and 7–8 respectively with significant amount of residual activities recorded. The purified pullulanase was stimulated in the presence of Ca²⁺, urea and SDS while Al³⁺, Fe²⁺, Co²⁺, Cu²⁺, Mg²⁺ and chelating agent, EDTA mildly inhibited the activity of the enzyme in a concentration-dependent manner. The K_m and V_max were found to be 0.324 μmol/ml/min and 6.85 mg/ml respectively. The exceptional physicochemical properties of B. safensis pullulanase could find application in several industrial processes.

Endo-xylanases from Cohnella sp. AR92 aimed at xylan and arabinoxylan conversion into value-added products

The genus Cohnella belongs to a group of Gram-positive endospore-forming bacteria within the Paenibacillaceae family. Although most species were described as xylanolytic bacteria, the literature still lacks some key information regarding their repertoire of xylan-degrading enzymes. The whole genome sequence of an isolated xylan-degrading bacterium Cohnella sp. strain AR92 was found to contain five genes encoding putative endo-1,4-β-xylanases, of which four were cloned, expressed, and characterized to better understand the contribution of the individual endo-xylanases to the overall xylanolytic properties of strain AR92. Three of the enzymes, CoXyn10A, CoXyn10C, and CoXyn11A, were shown to be effective at hydrolyzing xylans-derived from agro-industrial, producing oligosaccharides with substrate conversion values of 32.5%, 24.7%, and 10.6%, respectively, using sugarcane bagasse glucuronoarabinoxylan and of 29.9%, 19.1%, and 8.0%, respectively, using wheat bran-derived arabinoxylan. The main reaction products from GH10 enzymes were xylobiose and xylotriose, whereas CoXyn11A produced mostly xylooligosaccharides (XOS) with 2 to 5 units of xylose, often substituted, resulting in potentially prebiotic arabinoxylooligosaccharides (AXOS). The endo-xylanases assay displayed operational features (temperature optima from 49.9 to 50.4 °C and pH optima from 6.01 to 6.31) fitting simultaneous xylan utilization. Homology modeling confirmed the typical folds of the GH10 and GH11 enzymes, substrate docking studies allowed the prediction of subsites (- 2 to + 1 in GH10 and - 3 to + 1 in GH11) and identification of residues involved in ligand interactions, supporting the experimental data. Overall, the Cohnella sp. AR92 endo-xylanases presented significant potential for enzymatic conversion of agro-industrial by-products into high-value products.Key points• Cohnella sp. AR92 genome encoded five potential endo-xylanases.• Cohnella sp. AR92 enzymes produced xylooligosaccharides from xylan, with high yields.• GH10 enzymes from Cohnella sp. AR92 are responsible for the production of X2 and X3 oligosaccharides.• GH11 from Cohnella sp. AR92 contributes to the overall xylan degradation by producing substituted oligosaccharides.

Thermophilic iron containing type superoxide dismutase from Cohnella sp. A01

Superoxide dismutases (SODs) (EC 1.15.1.1) are well known antioxidant enzymes that play critical roles in cellular defenses of living organisms against harmful superoxide radicals during oxidative stress. This study details on cloning, biochemical and functional characterization of an iron containing type superoxide dismutase (SOD) from a novel thermophilic bacteria Cohnella sp. A01 (CaSOD). The secondary and three dimensional structure of the protein were predicted. CaSOD gene was subsequently cloned into pET-26b(+) expression vector and expression of the recombinant protein (rCaSOD) was optimized in E. coli BL21 (DE3) and the purified recombinant SOD showed a single band with an apparent molecular weight of 26 kDa by SDS-PAGE. The half-life and thermodynamic parameters including ΔH^⁎, ΔS^⁎, and ΔG^⁎ were 187 min at 60 °C, 7.3 kJ.mol^-1, -76.8 kJ.mol^-1.°K^-1, and 84.1 kJ.mol^-1, respectively. The rCaSOD exhibited catalytic activity in a very broad range of pH (6.0-10.0) and temperatures (35-75 °C), as well as stability in a broad pH range, from 3.0 to 11.0, and wide range of temperature, different concentrations of detergent agents, metal ions, organic solvents and other chemicals. The results suggest that this novel enzyme could be used for various industrial applications in cosmetic, food, and pharmaceutical industries.

Microbial starch debranching enzymes: Developments and applications

Starch debranching enzymes (SDBEs) hydrolyze the α-1,6 glycosidic bonds in polysaccharides such as starch, amylopectin, pullulan and glycogen. SDBEs are also important enzymes for the preparation of sugar syrup, resistant starch and cyclodextrin. As the synergistic catalysis of SDBEs and other starch-acting hydrolases can effectively improve the raw material utilization and production efficiency during starch processing steps such as saccharification and modification, they have attracted substantial research interest in the past decades. The substrate specificities of the two major members of SDBEs, pullulanases and isoamylases, are quite different. Pullulanases generally require at least two α-1,4 linked glucose units existing on both sugar chains linked by the α-1,6 bond, while isoamylases require at least three units of α-1,4 linked glucose. SDBEs mainly belong to glycoside hydrolase (GH) family 13 and 57. Except for GH57 type II pullulanse, GH13 pullulanases and isoamylases share plenty of similarities in sequence and structure of the core catalytic domains. However, the N-terminal domains, which might be one of the determinants contributing to the substrate binding of SDBEs, are distinct in different enzymes. In order to overcome the current defects of SDBEs in catalytic efficiency, thermostability and expression level, great efforts have been made to develop effective enzyme engineering and fermentation strategies. Herein, the diverse biochemical properties and distinct features in the sequence and structure of pullulanase and isoamylase from different sources are summarized. Up-to-date developments in the enzyme engineering, heterologous production and industrial applications of SDBEs is also reviewed. Finally, research perspective which could help understanding and broadening the applications of SDBEs are provided.

The Effect of Calcium/Magnesium Ratio on the Biomass Production of a Novel Thermoalkaliphilic Aeribacillus pallidus Strain with Highly Heat-Resistant Spores

Hot springs are fascinating extreme environments for the isolation of polyextremophilic microorganisms with extraordinary characteristics. Since polyextremophilic bacterial growth are not as high as routine bacteria, the objective of this study was to investigate the effect of some environmental factors on biomass and metabolites productions in the newly isolated strain, from Larijan hot spring in Iran. The strain was identified as Aeribacillus pallidus Lhs-10 and deposited as CCUG 72355 and IBRC-M 11202 in Sweden and Iran, respectively. This thermoalkaliphilic strain can grow best at 50 °C, pH 8 and in the presence of 25 g/l NaCl. The physiological characterization of this strain show that [Ca/Mg] ratio affect its growth and biomass production with the best results obtained at the ratio of 2.5. Moreover, lactic and acetic acids production by this strain was affected by pH, aeration, and temperature, where a metabolic shift was detected from lactate to acetate production when the culture was aerated. Besides, its spores could tolerate heating at 80, 85, 90, 95 and 98 °C for 30 min without any reduction in the initial spore population, whereas D-value was defined 50 min at 98 °C. This newly lactic acid-producing strain of A. pallidus can be a promising strain that can be used in the harsh conditions in industrial processes.

Novel halo- and thermo-tolerant Cohnella sp. A01 L-glutaminase: heterologous expression and biochemical characterization

L-glutaminase importance to use in the food industry and medicine has attracted much attention. Enzymes stability has always been a challenge while working with them. We heterologously expressed and characterized a novel stable L-glutaminase from an extremophile bacterium (Cohnella sp. A01, PTCC No: 1921). K_m, V_max, catalytic efficiency and specific activity of rSAM were respectively 1.8 mM, 49 µmol/min, 1851 1/(S.mM) and 9.2 IU/mg. Activation energy for substrate to product conversion and irreversible thermo-inactivation were respectively 4 kJ/mol and 105 kJ/mol from the linear Arrhenius plot. rSAM had the highest activity at temperature 50 °C, pH 8 and was resistant to a wide range of temperature and pH. In compare to the other characterized glutaminases, rSAM was the most resistant to NaCl. Mg²⁺, glycerol, DTT, and BME enhanced the enzyme activity and iodoacetate and iodoacetamide inhibited it. rSAM had only been partially digested by some proteases. According to the Fluorimetry and Circular dichroism analysis, rSAM in pH range from 4 to 11 and temperatures up to 60 °C had structural stability. A cysteine residue in the enzyme active site and a thiol bond were predicted upon the modeled tertiary structure of rSAM. Present structural studies also confirmed the presence of a thiol bond in its structure.

An amylopullulanase (ApuNP1) from Geobacillus thermoleovorans NP1: biochemical characterization and its potential industrial applications

An amylopullulanase was produced by Geobacillus thermoleovorans NP1. The optimum enzyme production occurred at 45°C and pH 7.0 (12 hr). NP1 amylopullulanase (ApuNP1) exhibited the maximal activity at 50°C and pH 6.0 and was stable between 30-50°C, and pH 3.0-12.0 for 24 hr. The enzyme showed two bands with molecular weights of 112 and 107 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The amylopullulanase retained 100% of its activity in the presence of 10 mM of Ca²⁺, Ba²⁺, Zn²⁺, Mg²⁺, Cu²⁺, EDTA, and PMSF. While the enzyme showed resistance to 5% of TritonX-100, Tween 20, and Tween 80, the activity was inhibited by 5% β-mercaptoethanol and H₂O₂. While the hydrolysis products of pullulan were maltose, maltotriose, and maltodextrin, the starch was hydrolyzed to maltose, maltotriose, and maltodextrin units. This shows that NP1 pullulanase is a type II pullulanase (amylopullulanase). After the liquefaction assay, 12% glucose content was measured with a refractometer in the presence of 20% starch. According to the wash performance tests, the mixture of ApuNP1 and 1% detergent removed almost all of the stains. This novel thermo-acidic amylopullulanase has a potency to be used in detergent, starch, food, baking, textile, and cosmetic industries.

Biochemical Characterization of Recombinant Thermostable Cohnella sp. A01 β-Glucanase

Background

Typically, non-cellulytic glucanase, including fungi and yeast cell wall hydrolyzing enzymes, are released by some symbiotic fungi and plants during the mycoparasitic fungi attack on plants. These enzymes are known as the defense mechanisms of plants. This study intends to investigate the biochemical properties of β-1,6-glucanase (bg16M) from native thermophilic bacteria, Cohnella A01.

Methods

bg16M gene was cloned and expressed in E. coli BL21 (DE3). The enzyme was purified utilizing Ni-NTA nikcle sepharose column. Pustulan and laminarin were selected as substrates in enzyme assay. The purified bg16M enzyme was treated with different pH, temperature, metal ions, and detergents.

Results

The expressed protein, including 639 amino acids, showed a high similarity with the hydrolytic glycosylated family 30. The molecular weight of enzyme was 64 kDa, and purification yield was 46%. The bg16M demonstrated activity as 4.83 U/ml on laminarin and 2.88 U/ml on pustulan. The optimum pH and temperature of the enzyme were 8 and 50 °C, respectively. The enzyme had an appropriate stability at high temperatures and in the pH range of 7 to 9, showing acceptable stability, while it did not lose enzymatic activity completely at acidic or basic pH. None of the studied metal ions and chemical compounds was the activator of bg16M, and urea, SDS, and copper acted as enzyme inhibitors.

Conclusion

Biochemical characterization of this enzyme revealed that bg16M can be applied in beverage industries and medical sectors because of its high activity, as well as thermal and alkaline stability.