Fermentative production of extracellular amylase from novel amylase producer,Tuber maculatum mycelium,and its characterization

Abstract

Truffles are symbiotic hypogeous edible fungi (form of mushroom) that form filamentous mycelia in their initial phase of the growth cycle as well as a symbiotic association with host plant roots. In the present study, Tuber maculatum mycelia were isolated and tested for extracellular amylase production at different pH on solid agar medium. Furthermore, the mycelium was subjected to submerged fermentation for amylase production under different culture conditions such as variable carbon sources and their concentrations, initial medium pH, and incubation time. The optimized conditions after the experiments included soluble starch (0.5% w/v), initial medium pH of 7.0, and incubation time of 7 days, at room temperature (22?±?2?°C) under static conditions which resulted in 1.41?U/mL of amylase. The amylase thus obtained was further characterized for its biocatalytic properties and found to have an optimum activity at pH 5.0 and a temperature of 50?°C. The enzyme showed good thermostability at 50?°C by retaining 98% of the maximal activity after 100?min of incubation. The amylase activity was marginally enhanced in presence of Cu²⁺ and Na⁺ and slightly reduced by K⁺, Ca²⁺, Fe²⁺, Mg²⁺, Co²⁺, Zn²⁺, and Mn²⁺ ions at 1?mM concentration.     

Mycelial amylase activities of thermophilic species ofRhizomucor,Humicola andPapulaspora

Amylase activities in mycelia ofRhizomucor pusillus, Humicola grisea var.thermoidea, Humicola lanuginosa andPapulaspora thermophilia do not correspond directly with previously-measured extracellular values, and appear to decline within the time period corresponding to reduction in mycelial dry weight. The results are compared with previously-reported data on extracellular amylase.     

Psychrophilic, mesophilic, and thermophilic triosephosphate isomerases from three clostridial species.

Triosephosphate isomerase was purified to homogeneity as judged by analytical gel electrophoresis from clostridium sp. strain 69, clostridium pasteurianum, and C. thermosaccharolyticum, which grow optimally at 18, 37, and 55 C, respectively. Comparative studies on these purified proteins showed that they had the same molecular weight (53,000) and subunit molecular weight (26,500). They were equally susceptible to the active site-directed inhibitor, glycidol phosphate. However, their temperature and pH optima, as well as their stabilities to heat, urea, and sodium dodecyl sulfate, differed. The proteins also had different mobilities in acrylamide gel electrophoresis. This difference in ionic character was also reflected in the elution behavior of the enzymes from hydroxyapatite and in the isoelectric points determined by isoelectric focusing in acrylamide gel. The amino acid composition of these proteins showed that the thermophilic enzyme contains a greater amount of proline than the other enzymes. The ratio of acidic amino acids to basic amino acids was 1.79, 1.38, and 1.66 for the thermophilic mesophilic and psychrophilic enzymes, respectively. This is consistent with the relative isoelectric point values of these three enzymes.     

Purification and characterization of an extracellular amylase from a thermophilic streptomycete

G oldberg , J.D. & E dwards , C. 1990. Purification and characterization of an extracellular amylase from a thermophilic streptomycete. Journal of Applied Bacteriology 69 , 712–717.
A single extracellular alpha-amylase (1,4-α-D-glucan glucanohydrolase, EC 3.2.1.1) from Streptomyces thermoviolaceus subsp. apingens was purified to homogeneity by a starch adsorption method. SDS-PAGE indicated that the enzyme had an apparent M, of 57 kDa and activity was optimal at a pH of 7–2 and a temperature of 55C. It employed an endo-active mechanism to liberate predominantly maltose, as well as smaller amounts of higher oligosaccharides when incubated with starch. EDTA inhibited enzyme activity, suggesting an involvement of a divalent cation in activity. The enzyme was also stabilized by divalent cations when heated and the results suggested a major role for Ca²⁺ ions for both activity and thermostability. The alpha-amylase from S. thermoviolaceus displayed some similarities with commercially-used streptomycete alpha-amylases.     

The thermostability of DNA-binding protein HU from mesophilic, thermophilic, and extreme thermophilic bacteria

Based on primary structure comparison between four highly homologous DNA-binding proteins (HUs) displaying differential thermostability, we have employed in vitro site-directed mutagenesis to decipher their thermostability mechanism at the molecular level. The contribution of the 11 amino acids that differ between the thermophilic HUBst from Bacillus stearothermophilus (Tm = 61.6 degrees C) and the mesophilic HUBsu from Bacillus subtilis (Tm = 39.7 degrees C) was evaluated by replacing these amino acids in HUBst with their mesophilic counterparts. Among 11 amino acids, three residues, Gly-15, Glu-34, and Val-42, which are highly conserved in the thermophilic HUs, have been found to be responsible for the thermostability of HUBst. These amino acids in combination (HUBst-G15E/E34D/V42I) reduce the thermostability of the protein (Tm = 45.1 degrees C) at the level of its mesophilic homologue HUBsu. By replacing these amino acids in HUBsu with their thermophilic counterparts, the HUBsu-E15G/D34E/142V mutant was generated with thermostability (Tm = 57.8 degrees C) at the level of thermophilic HUBst. Employing the same strategy, we generated several mutants in the extremely thermophilic HUTmar from Thermotoga maritima (Tm = 80.5 degrees C), and obtained data consistent with the previous results. The triplet mutant HUTmar-G15E/E34D/V421 (Tm = 35.9 degrees C) converted the extremely thermophilic protein HUTmar to mesophilic. The various forms of HU proteins were overproduced in Escherichia coli, highly purified, and the thermostability of the mutants confirmed by circular dichroism spectroscopy. The results presented here were elucidated on the basis of the X-ray structure of HUBst and HUTmar (our unpublished results), and their mechanism was proposed at the molecular level. The results clearly show that three individual local interactions located at the helix-turn-helix part of the protein are responsible for the stability of HU proteins by acting cooperatively in a common mechanism for thermostability.     

The specific activities of mesophilic and thermophilic proteinases

1. Most enzymes from extreme thermophiles do not possess higher specific activities than similar enzymes from mesophiles (measured at their respective growth temperatures). 2. However, using protein substrates, the specific activities of thermophilic proteinases are considerably higher than those of most microbial and eukaryotic proteinases. 3. This property could be attributed to purely kinetic influences on the enzyme, to some specific "design" feature of the proteinase, or to the effects of temperature on the substrate. 4. Comparisons of the rates of hydrolysis of large and small substrates by both mesophilic and thermophilic proteinases suggest that temperature-induced changes in substrate susceptibility are a major factor.     

Isocitrate dehydrogenase from thermophilic and mesophilic bacteria. Isolation and some characteristics

1. Simple methods incorporating the principle of selective enzyme elution from a triazinyl dye adsorbent with a mixture of NADP+ and isocitrate are described for isolating NADP+-linked isocitrate dehydrogenase in pure state from several mesophilic and thermophilic bacteria. 2. Several characteristics of the isocitrate dehydrogenases have been examined, viz. molecular size, amino acid composition including the content of sulphydryl groups, thermostability and structural homology by the criterion of immunological cross-section.     

Discrimination of thermophilic and mesophilic proteins

Background

There is a considerable literature on the source of the thermostability of proteins from thermophilic organisms. Understanding the mechanisms for this thermostability would provide insights into proteins generally and permit the design of synthetic hyperstable biocatalysts.

Results

We have systematically tested a large number of sequence and structure derived quantities for their ability to discriminate thermostable proteins from their non-thermostable orthologs using sets of mesophile-thermophile ortholog pairs. Most of the quantities tested correspond to properties previously reported to be associated with thermostability. Many of the structure related properties were derived from the Delaunay tessellation of protein structures.

Conclusions

Carefully selected sequence based indices discriminate better than purely structure based indices. Combined sequence and structure based indices improve performance somewhat further. Based on our analysis, the strongest contributors to thermostability are an increase in ion pairs on the protein surface and a more strongly hydrophobic interior.

     

Multiple time scale backbone dynamics of homologous thermophilic and mesophilic ribonuclease HI enzymes

Backbone conformational fluctuations on multiple time scales in a cysteine-free Thermus thermophilus ribonuclease HI mutant (ttRNH(*)) are quantified using (15)N nuclear magnetic spin relaxation. Laboratory-frame relaxation data acquired at 310 K and at static magnetic field strengths of 11.7, 14.1 and 18.8 T are analysed using reduced spectral density mapping and model-free approaches. Chemical exchange line broadening is characterized using Hahn-echo transverse and multiple quantum relaxation data acquired over a temperature range of 290-320 K and at a static magnetic field strength of 14.1 T. Results for ttRNH(*) are compared to previously published data for a mesophilic homologue, Escherichia coli ribonuclease HI (ecRNH). Intramolecular conformational fluctuations on the picosecond-to-nanosecond time scale generally are similar for ttRNH(*) and ecRNH. beta-Strands 3 and 5 and the glycine-rich region are more rigid while the substrate-binding handle region and C-terminal tail are more flexible in ttRNH(*) than in ecRNH. Rigidity in the two beta-strands and the glycine-rich region, located along the periphery of the central beta-sheet, may be associated with the increased thermodynamic stability of the thermophilic enzyme. Chemical exchange line broadening, reflecting microsecond-to-millisecond time scale conformational changes, is more pronounced in ttRNH(*) than in ecRNH, particularly for residues in the handle and surrounding the catalytic site. The temperature dependence of chemical exchange show an increase of approximately 15 kJ/mol in the apparent activation energies for ttRNH(*) residues in the handle compared to ecRNH. Increased activation barriers, coupled with motion between alpha-helices B and C not present in ecRNH, may be associated with the reduced catalytic activity of the thermophilic enzyme at 310 K.     

Temperature adaptations in psychrophilic, mesophilic and thermophilic chloride-dependent alpha-amylases

The functional and structural adaptations to temperature have been addressed in homologous chloride-dependent α-amylases from a psychrophilic Antarctic bacterium, the ectothermic fruit fly, the homeothermic pig and from a thermophilic actinomycete. This series covers nearly all temperatures encountered by living organisms. We report a striking continuum in the functional properties of these enzymes coupled to their structural stability and related to the thermal regime of the source organism. In particular, thermal stability recorded by intrinsic fluorescence, circular dichroism and differential scanning calorimetry appears to be a compromise between the requirement for a stable native state and the proper structural dynamics to sustain the function at the environmental/physiological temperatures. The thermodependence of activity, the kinetic parameters, the activations parameters and fluorescence quenching support these activity-stability relationships in the investigated α-amylases.     

Intracellular protein breakdown in thermophilic and mesophilic fungi

1. The rate of protein breakdown was determined on growing and non-growing cultures of thermophilic and mesophilic fungi. 2. In growing cells protein breakdown was negligible. 3. In non-growing cells the breakdown rate of total protein varied between 5.2%/h and 6.7%/h. These values were found to be dependent on both the temperature of the protein breakdown assay and the temperature of growth of the organism. 4. The rate of breakdown of soluble protein in thermophilic fungi was 9-15%/h whereas the rate in mesophilic fungi for the soluble protein fraction was only 4%/h.     

Structural equilibrium fluctuations in mesophilic and thermophilic alpha-amylase

By comparing a mesophilic alpha-amylase with its thermophilic homolog, we investigated the relationship between thermal stability and internal equilibrium fluctuations. Fourier transform infrared spectroscopy monitoring hydrogen/deuterium (H/D) exchange kinetics and incoherent neutron scattering measuring picosecond dynamics were used to study dynamic features of the folded state at room temperature. Fairly similar rates of slowly exchanging amide protons indicate about the same free energy of stabilization DeltaG(stab) for both enzymes at room temperature. With respect to motions on shorter time scales, the thermophilic enzyme is characterized by an unexpected higher structural flexibility as compared to the mesophilic counterpart. In particular, the picosecond dynamics revealed a higher degree of conformational freedom for the thermophilic alpha-amylase. The mechanism proposed for increasing thermal stability in the present case is characterized by entropic stabilization and by flattening of the curvature of DeltaG(stab) as a function of temperature.     

Comparative study of energy-transducing properties of cytoplasmic membranes from mesophilic and thermophilic Bacillus species.

The properties of enzymes involved in energy transduction from a mesophilic (Bacillus subtilis) and a thermophilic (B. stearothermophilus) bacterium were compared. Membrane preparations of the two organisms contained dehydrogenases for NADH, succinate, L-alpha-glycerophosphate, and L-lactate. Maximum NADH and cytochrome c oxidation rates were obtained at the respective growth temperatures of the two bacteria. The enzymes involved in the oxidation reactions in membranes of the thermophilic species were more thermostable than those of the mesophilic species. The apparent microviscosities of the two membrane preparations were studied at different temperatures. At the respective optimal growth temperatures, the apparent microviscosities of the membranes of the two organisms were remarkably similar. The transition from the gel to the liquid-crystalline state occurred at different temperatures in the two species. In the two species, the oxidation of physiological (NADH) and nonphysiological (N,N,N',N'-tetramethyl-p-phenylenediamine or phenazine methosulfate) electron donors led to generation of a proton motive force which varied strongly with temperature. At increasing temperatures, the efficiency of energy transduction declined because of increasing H+ permeability. At the growth temperature, the efficiency of energy transduction was lower in B. stearothermophilus than in the mesophilic species. Extremely high respiratory activities enabled B. stearothermophilus to maintain a high proton motive force at elevated temperatures. The pH dependence of proton motive force generation appeared to be similar in the two membrane preparations. The highest proton motive forces were generated at low external pH, mainly because of a high pH gradient. At increasing external pH, the proton motive force declined.     

Studies on the extracellular xylanase activity of some thermophilic actinomycetes

Summary An agar plate-clearing assay was used to screen 37 thermophilic actinomycete strains for extracellular xylanase production. The xylanase activity in culture supernatants of strains representing Saccharomonospora viridis and three Thermomonospora spp. was characterised by measurement of reducing sugar released from oat spelt xylan and analysis of degradation products by thin-layer chromatography. In all four species, xylanase activity was optimal within the temperature range 60–75°C and between pH 5 and pH 8. While culture supernatants of Thermomonospora strains incubated at 70°C for 60 min retained >80% of their activity, that of S. viridis was almost, totally inactivated.All of the culture supernatants initially hydrolysed xylan to a mixture of oligomeric products, indicating that the main activity was of the endoxylanase type. Prolonged incubation for 24h resulted in the hydrolysis of xylan to d-xylose by T curvata and T. fusca preparations, indicating the additional presence of exoxylanase or -xylosidase activity. Xylanase production was induced by growth on xylan although low levels of activity were also detected in glucose-grown cultures. Thermomonospora curvata MT815 culture supernatant was the most active and produced d-xylose from milled wheat straw in yields approximately 10% of those from oat spelt xylan.     

Properties of an extracellular amylase purified from a Bacillus species

A strain of Bacillus produced an amylase with properties characteristically different from known bacterial amylases. The purified 80 kDa protein of pI 5.1 dextrinized starch, glycogen and pullulan. The temperature and pH optima of the enzyme were 60 °C and 6.6 respectively. In the presence of 0.05 M CaCl₂, the enzyme retained stability for 15 min at 80 °C. Antibodies raised to the amylase protein showed no reaction with -amylases of Bacillus sp. and B. licheniformis. In culture, proteolytic degradation of the enzyme was observed.