Enzymes involved in the processing of starch to sugars

Affinity covalent immobilization of glucoamylase onto ρ-benzoquinone activated alginate beads: I. Beads preparation and characterization

ρ-Benzoquinone-activated alginate beads were presented as a new carrier for affinity covalent immobilization of glucoamylase enzyme. Evidences of alginate modification were extracted from FT-IR and thermal gravimetric analysis and supported by morphological changes recognized through SEM examination. Factors affecting the modification process such as ρ-benzoquinone (PBQ) concentration, reaction time, reaction temperature, reaction pH and finally alginate concentration, have been studied. Its influence on the amount of coupled PBQ was consequently correlated to the changes of the catalytic activity and the retained activity of immobilized enzyme, the main parameters judging the success of the immobilization process. The immobilized glucoamylase was found kept almost 80% of its native activity giving proof of non-significant substrate, starch, diffusion limitation. The proposed affinity covalent immobilizing technique would rank among the potential strategies for efficient immobilization of glucoamylase enzyme.

Magnetically recyclable, antimicrobial, and catalytically enhanced polymer-assisted "green" nanosystem-immobilized Aspergillus niger amyloglucosidase

The present work reports the integration of polymer matrix-supported nanomaterial and enzyme biotechnology for development of industrially feasible biocatalysts. Aqueous leaf extract of Mesua ferrea L. was used to prepare silver nanoparticles distributed within a narrow size range (1-12 nm). In situ oxidative technique was used to obtain poly(ethylene glycol)-supported iron oxide nanoparticles (3-5 nm). Sonication-mediated mixing of above nanoparticles generated the immobilization system comprising of polymer-supported silver-iron oxide nanoparticles (20-30 nm). A commercially important enzyme, Aspergillus niger amyloglucosidase was coupled onto the immobilization system through sonication. The immobilization enzyme registered a multi-fold increment in the specific activity (807 U/mg) over the free counterpart (69 U/mg). Considerable initial activity of the immobilized enzyme was retained even after storing the system at room temperature as well as post-repeated magnetic recycling. Evaluation of the commendable starch saccharification rate, washing performance synergy with a panel of commercial detergents, and antibacterial potency strongly forwards the immobilized enzyme as a multi-functional industrially feasible system.

Effective solubilization and single-step purification of Bacillus licheniformis alpha-amylase from insoluble aggregates

A high level expression of thermostable alpha-amylase gene from Bacillus licheniformis in Escherichia coli was obtained. The recombinant enzyme was mainly produced in the form of insoluble aggregates. The enzyme was solubilized without using denaturing agents and purified to homogeneity in a single step by ion exchange chromatography. The enzyme was purified 138-fold with a final yield of 349 %; the specific activity of the purified enzyme was 1343 U/mg.

A selection that reports on protein-protein interactions within a thermophilic bacterium

Many proteins can be split into fragments that exhibit enhanced function upon fusion to interacting proteins. While this strategy has been widely used to create protein-fragment complementation assays (PCAs) for discovering protein-protein interactions within mesophilic organisms, similar assays have not yet been developed for studying natural and engineered protein complexes at the temperatures where thermophilic microbes grow. We describe the development of a selection for protein-protein interactions within Thermus thermophilus that is based upon growth complementation by fragments of Thermotoga neapolitana adenylate kinase (AK(Tn)). Complementation studies with an engineered thermophile (PQN1) that is not viable above 75 degrees C because its adk gene has been replaced by a Geobacillus stearothermophilus ortholog revealed that growth could be restored at 78 degrees C by a vector that coexpresses polypeptides corresponding to residues 1-79 and 80-220 of AK(Tn). In contrast, PQN1 growth was not complemented by AK(Tn) fragments harboring a C156A mutation within the zinc-binding tetracysteine motif unless these fragments were fused to Thermotoga maritima chemotaxis proteins that heterodimerize (CheA and CheY) or homodimerize (CheX). This enhanced complementation is interpreted as arising from chemotaxis protein-protein interactions, since AK(Tn)-C156A fragments having only one polypeptide fused to a chemotaxis protein did not complement PQN1 to the same extent. This selection increases the maximum temperature where a PCA can be used to engineer thermostable protein complexes and to map protein-protein interactions.

Production and properties of α-amylase fromBacillussp. BKL20

As a result of screening Bacillus sp. strains isolated from different natural substrates, strain BKL20 was identified as a producer of a thermostable alkaline α-amylase. Maximum production of this α-amylase was achieved by optimizing culture conditions. Production of α-amylase seemed to be independent of the presence of starch in the culture medium and was stimulated by the presence of peptone (0.3%, m/v) and yeast extract (0.2%, m/v). The enzyme was thermostable and retained amylolytic activity after 30 min of incubation at 60 and 70 °C. High activity was maintained over a broad pH range, from 6.0 to 11.0, and the enzyme remained active after alkaline incubation for 24 h. Bacillus sp. BKL20 α-amylase was not stimulated by Ca2+or other bivalent metal cations and was not inhibited by EGTA or EDTA at 1–10 mmol/L, suggesting that this α-amylase is a Ca2+-independent enzyme. It also showed good resistance to both oxidizing (H2O2) and denaturating (urea) agents.

Plant cell calcium-rich environment enhances thermostability of recombinantly produced alpha-amylase from the hyperthermophilic bacterium Thermotoga maritime

In the industrial processing of starch for sugar syrup and ethanol production, a liquefaction step is involved where starch is initially solubilized at high temperature and partially hydrolyzed with a thermostable and thermoactive alpha-amylase. Most amylases require calcium as a cofactor for their activity and stability, therefore calcium, along with the thermostable enzyme, are typically added to the starch mixture during enzymatic liquefaction, thereby increasing process costs. An attractive alternative would be to produce the enzyme directly in the tissue to be treated. In a proof of concept study, tobacco cell cultures were used as model system to test in planta production of a hyperthermophilic alpha-amylase from Thermotoga maritima. While comparable biochemical properties to recombinant production in Escherichia coli were observed, thermostability of the plant-produced alpha-amylase benefited significantly from high intrinsic calcium levels in the tobacco cells. The plant-made enzyme retained 85% of its initial activity after 3 h incubation at 100 degrees C, whereas the E. coli-produced enzyme was completely inactivated after 30 min under the same conditions. The addition of Ca(2+) or plant cell extracts from tobacco and sweetpotato to the E. coli-produced enzyme resulted in a similar stabilization, demonstrating the importance of a calcium-rich environment for thermostability, as well as the advantage of producing this enzyme directly in plant cells where calcium is readily available.

Characterisation of fermentation of high-gravity maize mashes with the application of pullulanase, proteolytic enzymes and enzymes degrading non-starch polysaccharides

The aim of the research was to assess the possibility of the fermentation productivity rising through the increase in corn mashes extract from 16-17 to 20-21 degrees Balling, yet keeping a 3-day fermentation period. The second goal was to obtain the highest possible utilization of starch in the raw material through deep enzymatic degradation and utilization of available sugars and simultaneous maintenance of high quality spirit. It was found that fulfilling the above during the 3-day fermentation period was possible with the application of pullulanase as an additional amylolytic enzyme. Adding pullulanase resulted in the acceleration of the starch hydrolysis degree, which led to lower amounts of unhydrolyzed dextrins and higher ethanol yield. When the supportive enzymes complex (pullulanase, protease and cellulase) was used, the final ethanol concentration reached 10.86+/-0.04% v/v, with ethanol yield at 68.41+/-0.23 dm(3) of absolute ethanol (A(100)) per 100 kg of starch, which was 95.25+/-0.32% at the theoretical value. The acceleration of starch enzymatic degradation and the application of a proteolytic preparation visibly shortened both initial and main fermentation phases. This in turn increased the time of the final fermentation phase and resulted in more extensive utilization of substrates by yeasts with simultaneous reduction of the final concentration of acetaldehyde (26.0+/-0.5 mg/dm(3)A(100)) and diethyl acetal of acetaldehyde (2.5+/-0.5 mg/dm(3)A(100)). The quality of spirit obtained was positively verified also in terms of relatively low concentration of higher alcohol (3912.2+/-9.8 mg/dm(3)A(100)). Preliminary analysis of costs (without raw-material) of 1 l distillate production indicated the possibility to reduce the costs by 18-20%.

Mutagenesis and genetic characterisation of amylolytic Aspergillus niger

Aspergillus niger FCBP-198 was genetically modified for its ability to reveal extra cellular alpha-amylase enzyme activity. From 76 efficient mutants isolated after ultraviolet (UV) irradiation, An-UV-5.6 was selected as the most efficient UV mutant, with 76.41 units mL(-1) of alpha-amylase activity compared to wild (34.45 units mL(-1)). In case of ethyl methane sulphonate (EMS), among 242 survivors, 74 were assayed quantitatively and An-Ch-4.7 was found to be the most competent, as it exhibited a three-fold increase in alpha-amylase activity (89.38 units mL(-1)) than the parental strain. Genetic relationships of the mutants of A. niger FCBP-198 were analysed with a randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Results obtained from the comparison between genotypes of A. niger FCBP-198 showed differences in the sizes and numbers of amplified fragments per primer for each isolate. The dendrogram showed that genotypes An-Ch-4.7 and An-Ch-4.2 were distinctly classified into one category, while the isolates An-UV-5.6, An-UV-5.1 and A. niger FCBP-198 have the nearest genetic relationship. The five isolates from A. niger FCBP-198 genotypes shared an average of 65% bands.

Hyperthermostable, Ca(2+)-independent, and high maltose-forming alpha-amylase production by an extreme thermophile Geobacillus thermoleovorans: whole cell immobilization

The synthesis of extracellular alpha-amylase in Geobacillus thermoleovorans was constitutive. The enzyme was secreted in metabolizable carbon sources as well as non-metabolizable synthetic analogues of glucose, but the titers were higher in the former than that in the latter. G. thermoleovorans is a fast-growing facultatively anaerobic bacterium that grows under both aerobic and anaerobic conditions and produces an extracellular amylolytic enzyme alpha-amylase with the by-product of lactic acid. G. thermoleovorans is a rich source of various novel thermostable biocatalysts for different industrial applications. alpha-Amylase synthesis was subject to catabolite repression in the presence of high concentrations of glucose. The addition of cAMP to the medium containing glucose did not result in the repression of alpha-amylase synthesis. The addition of maltose (1%) to the starch arginine medium resulted in a twofold enhancement in enzyme titers. Polyurethane foam (PUF)-immobilized cells secreted alpha-amylase, which was higher than that with the free cells. PUF appeared to be a better matrix for immobilization of the thermophilic bacterium than the other commonly used matrices. The repeated use of PUF-immobilized cells was possible over 15 cycles with a sustained alpha-amylase secretion. The use of this enzyme in starch saccharification eliminates the addition of Ca(2+) in starch liquefaction and its subsequent removal by ion exchangers from the product streams.

Synthesis of a mesoporous functional copolymer bead carrier and its properties for glucoamylase immobilization

A series of mesoporous and hydrophilic novel bead carriers containing epoxy groups were synthesized by modified inverse suspension polymerization. Glycidyl methacrylate and acryloyloxyethyl trimethyl ammonium chloride were used as the monomers, and divinyl benzene, allyl methacrylate, and ethylene glycol dimethacrylate as crosslinking agents, respectively. The resulting carriers were employed in the immobilization of glucoamylase (Glu) with covalent bond between epoxy groups and enzymes. The activity recovery of the three series of immobilized Glus could reach 76%, 79%, and 86%, respectively. The immobilized Glus exhibit excellent stability and reusability than that of the free ones.

Accelerated Biocatalyst Stability Testing for Process Optimization

The deactivation of protein biocatalysts even at relatively low temperatures is one of the principal drawbacks to their use. To aid in the development of novel biocatalysts, we have derived an equation for both time- and temperature-dependent activity of the biocatalyst based on known concepts such as transition state theory and the Lumry-Eyring model. We then derived an analytical solution for the total turnover number (ttn), under isothermal operation, as a function of the catalytic constant kcat, the unfolding equilibrium constant K, and the intrinsic first-order deactivation rate constant(s) k(d,i). Employing an immobilized glucose isomerase biocatalyst in a CSTR and utilizing a linear temperature ramp beyond the Tm of the enzyme, we demonstrate an accelerated method for extracting the thermodynamic and kinetic constants describing the biocatalyst system. In addition, we demonstrate that the predicted biocatalyst behavior at different temperatures and reaction times is consistent with the experimental observations.

Overproduction of glucoamylase by a deregulated mutant of a thermophilic mould Thermomucor indicae-seudaticae

Thermomucor indicae-seudaticae, a glucoamylase-producing thermophilic mould, was mutagenised using nitrous acid and gamma ((60)Co) irradiation in a sequential manner to isolate deregulated mutants for enhanced production of glucoamylase. The mutants were isolated on Emerson YpSs agar containing a non-metabolisable glucose analogue 2-deoxy-D-glucose (2-DG) for selection. The preliminary screening for glucoamylase production using starch-iodine plate assay followed by quantitative confirmation in submerged fermentation permitted the isolation of several variants showing varying levels of derepression and glucoamylase secretion. The mutant strain T. indicae-seudaticae CR19 was able to grow in the presence of 0.5 g l(-1) 2-DG and produced 1.8-fold higher glucoamylase. As with the parent strain, glucoamylase production by T. indicae-seudaticae CR19 in 250-ml Erlenmeyer flasks attained a peak in 48 h of fermentation, showing higher glucoamylase productivity (0.67 U ml(-1) h(-1)) than the former (0.375 U ml(-1) h(-1)). A large-scale cultivation in 5-l laboratory bioreactor confirmed similar fermentation profiles, though the glucoamylase production peak was attained within 36 h attributable to the better control of process parameters. Although the mutant grew slightly slow in the presence of 2-DG and exhibited less sporulation, it showed faster growth on normal Emerson medium with a higher specific growth rate (0.138 h(-1)) compared to the parent strain (0.123 h(-1)). The glucoamylase produced by both strains was optimally active at 60 degrees C and pH 7.0 and displayed broad substrate specificity by cleaving alpha-1,4- and alpha-1,6-glycosidic linkages in starch, amylopectin, amylose and pullulan. Improved productivity and higher specific growth rate make T. indicae-seudaticae CR19 a useful strain for glucoamylase production.

Purification and characterization of a hyperthermostable and high maltogenic alpha-amylase of an extreme thermophile Geobacillus thermoleovorans

The purified alpha-amylase of Geobacillus thermoleovorans had a molecular mass of 26 kDa with a pI of 5.4, and it was optimally active at 100 degrees C and pH 8.0. The T 1/2 of alpha-amylase at 100 degrees C increased from 3.6 to 5.6 h in the presence of cholic acid. The activation energy and temperature quotient (Q 10) of the enzyme were 84.10 kJ/mol and 1.31, respectively. The activity of the enzyme was enhanced strongly by Co2+ and Fe2+; enhanced slightly by Ba2+, Mn2+, Ni2+, and Mg2+; inhibited strongly by Sn2+, Hg2+, and Pb2+, and inhibited slightly by EDTA, phenyl methyl sulfonyl fluoride, N-ethylmaleimide, and dithiothreitol. The enzyme activity was not affected by Ca2+ and ethylene glycol-bis (beta-amino ethyl ether)-N,N,N,N-tetra acetic acid. Among different additives and detergents, polyethylene glycol 8000 and Tween 20, 40, and 80 stabilized the enzyme activity, whereas Triton X-100, glycerol, glycine, dextrin, and sodium dodecyl sulfate inhibited to a varied extent. alpha-Amylase exhibited activity on several starch substrates and their derivatives. The K m and K cat values (soluble starch) were 1.10 mg/ml and 5.9 x 10(3)/min, respectively. The enzyme hydrolyzed raw starch of pearl millet (Pennisetum typhoides) efficiently.

Enhancement of acid amylase production by an isolated Aspergillus awamori

AIMS

Evaluation of the influence of fermentation components on extracellular acid amylase production by an isolated fungal strain Aspergillus awamori.

METHODS AND RESULTS

Eight fungal metabolic influential factors, viz. soluble starch, corn steep liquor (CSL), casein, potassium dihydrogen phosphate (KH(2)PO(4)) and magnesium sulfate (MgSO(4) x 7H(2)O), pH, temperature and inoculum level were selected to optimize amylase production by A. awamori using fractional factorial design of Taguchi methodology. Significant improvement in acid amylase enzyme production (48%) was achieved. The optimized medium composition consisted of soluble starch--3%; CSL--0.5%; KH(2)PO(4)--0.125%; MgSO(4) x 7H(2)O--0.125%; casein--1.5% at pH 4.0 and temperature at 31 degrees C.

CONCLUSION

Optimization of the components of the fermentation medium was carried out using fractional factorial design of Taguchi's L-18 orthogonal array. Based on the influence of interaction components of fermentation, these could be classified as the least significant and the most significant at individual and interaction levels. Least significant factors of individual level have higher interaction severity index and vice versa at enzyme production in this fungal strain. The pH of the medium and substrate (soluble starch) showed maximum production impact (60%) at optimized environment. Temperature and CSL were the least influential factors for acid amylase production.

SIGNIFICANCE AND IMPACT OF THE STUDY

Acid amylase production by isolated A. awamori is influenced by the interaction of fermentation factors with fungal metabolism at individual and interaction levels. The pH of the fermentation medium and substrate concentration regulates maximum enzyme production process in this fungal strain.

Potential and utilization of thermophiles and thermostable enzymes in biorefining

In today's world, there is an increasing trend towards the use of renewable, cheap and readily available biomass in the production of a wide variety of fine and bulk chemicals in different biorefineries. Biorefineries utilize the activities of microbial cells and their enzymes to convert biomass into target products. Many of these processes require enzymes which are operationally stable at high temperature thus allowing e.g. easy mixing, better substrate solubility, high mass transfer rate, and lowered risk of contamination. Thermophiles have often been proposed as sources of industrially relevant thermostable enzymes. Here we discuss existing and potential applications of thermophiles and thermostable enzymes with focus on conversion of carbohydrate containing raw materials. Their importance in biorefineries is explained using examples of lignocellulose and starch conversions to desired products. Strategies that enhance thermostablity of enzymes both in vivo and in vitro are also assessed. Moreover, this review deals with efforts made on developing vectors for expressing recombinant enzymes in thermophilic hosts.

Effect of aniline coupling on kinetic and thermodynamic properties of Fusarium solani glucoamylase

Purified glucoamylase (GA) from Fusarium solani was chemically modified by cross-linking with aniline hydrochloride in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) for 1 [aniline-coupled glucoamylase-1 (ACG-1)], 7 (ACG-7), and 13 min (ACG-13). The aniline coupling of GA had a profound enhancing effect on temperature, pH optima, and pK (a)'s of active site residues. The specificity constants (K (cat)/K (m)) of native, ACG-1, ACG-7, and ACG-13 were 136, 244, 262, and 208 at 55 degrees C for starch, respectively. The enthalpy of activation (DeltaH*) and free energy of activation (DeltaG*) for soluble starch hydrolysis were lower for the chemically modified forms compared to native GA. Proteolysis of ACGs by alpha-chymotrypsin and subtilisin resulted in activation.

Efficient solubilization, purification of recombinant extracellular α-amylase from pyrococcus furiosus expressed as inclusion bodies in Escherichia coli

The gene encoding the Pyrococcus furiosus extracellular alpha-amylase (PFA) was amplified by PCR from P. furiosus genomic DNA and was highly expressed in Escherichia coli BL21-Codon Plus (DE3)-RIL. The recombinant alpha-amylase was mainly expressed in the form of insoluble inclusion bodies. An improved purification method was established in this paper. The solubilization of the inclusion bodies was achieved by 90 degrees C treatment for 3 min in Britton-Robinson buffer at pH 10.5. The solubilized PFA was then diluted and subsequently purified by Phenyl Sepharose chromatography. The overall yield of the new purification method was about 58,000 U/g wet cells, which is higher than previously reported.

Comparison of the wild-type alpha-amylase and its variant enzymes in Bacillus amyloliquefaciens in activity and thermal stability, and insights into engineering the thermal stability of bacillus alpha-amylase

The starch hydrolysis activity and thermal stability of Bacillus amyloliquefaciens alpha-amylase (wild-type enzyme or WT) and its variant enzymes, designated as M77, M111, and 21B, were compared. All have an optimal pH at around 6, as well as almost the same reaction rates and Km and kcat values. The optimal temperature in the absence of Ca2+ ions is 60 degrees C for WT and M77 and 40 degrees C for M111 and 21B. Those of M111 and 21B rose to 50-60 degrees C upon the addition of 5 mM CaCl2, while those of WT and M77 did not change. The dissociation constants Kd for Ca2+ to WT and M77 are much lower than those of M111 and 21B. Asp233 in WT is replaced by Asn in M111 and 21B, while it is retained in M77, suggesting that Asp233 is involved in the thermal stability of the enzyme through Ca2+ ion binding. These findings provide insight into engineering the thermal stability of B. amyloliquefaciens alpha-amylase, which would be useful for its applications in the baking industry and in glucose manufacturing.

Enhancing thermostability of maltogenic amylase from Bacillus thermoalkalophilus ET2 by DNA shuffling

DNA shuffling was used to improve the thermostability of maltogenic amylase from Bacillus thermoalkalophilus ET2. Two highly thermostable mutants, III-1 and III-2, were generated after three rounds of shuffling and recombination of mutations. Their optimal reaction temperatures were all 80 degrees C, which was 10 degrees C higher than that of the wild-type. The mutant enzyme III-1 carried seven mutations: N147D, F195L, N263S, D311G, A344V, F397S, and N508D. The half-life of III-1 was about 20 times greater than that of the wild-type at 78 degrees C. The mutant enzyme III-2 carried M375T in addition to the mutations in III-1, which was responsible for the decrease in specific activity. The half-life of III-2 was 568 min while that of the wild-type was < 1 min at 80 degrees C. The melting temperatures of III-1 and III-2, as determined by differential scanning calorimetry, increased by 6.1 degrees C and 11.4 degrees C, respectively. Hydrogen bonding, hydrophobic interaction, electrostatic interaction, proper packing, and deamidation were predicted as the mechanisms for the enhancement of thermostability in the enzymes with the mutations.

Comparison of Starch Hydrolysis Activity and Thermal Stability of Two Bacillus licheniformis α-Amylases and Insights into Engineering α-Amylase Variants Active under Acidic Conditions

Bacillus licheniformis alpha-amylase (BLA) is widely used in various procedures of starch degradation in the food industry, and a BLA species with improved activity at higher temperature and under acidic conditions is desirable. Two BLA species, designated as PA and MA, have been isolated from the wild-type B. licheniformis strain and a mutant strain, respectively. In this study, their starch-hydrolysis activity and thermal stability were examined. MA showed higher activity than PA, especially at acidic pH (pH 5.0-5.5), and even after 1 h of treatment at 90 degrees C. MA was active in the range of pH 4.0-8.0, which is much wider than that (pH 4.5-7.5) of PA. It was shown that the proton dissociation constants on the acidic and alkaline sides (pKa1 and pKa2) were shifted to more acidic and basic values, respectively, by the mutation of PA to MA. The activation energy and thermodynamic parameters for their thermal inactivation indicate that MA is more thermally stable and catalytically active than PA, suggesting that MA could be useful for glucose-production process coupled with reactions catalyzed by beta-amylase.

Potential role of glycosidase inhibitors in industrial biotechnological applications

The nutrient content of food and animal feed may be improved through new knowledge about enzymatic changes in complex carbohydrates. Enzymatic hydrolysis of complex carbohydrates containing alpha or beta glycosidic bonds is very important in nutrition and in several technological processes. These enzymes are called glycosidases (Enzyme Class 3.2.1) and include amylases, pectinases and xylanases. They are present in many foods such as cereals, but their microbial analogues are often produced and added in many food processes, for instance to improve the shelf-life of bakery products, clear beer, produce glucose, fructose or dextrins, hydrolyse lactose, modify food pectins, or improve processes. However, many plant foods also contain endogenous inhibitors, which reduce the activity of glycosidases, in particular, proteins, peptides, complexing agents and phenolic compounds. The plant proteinaceous inhibitors of glycosidases are in focus in this review whose objective is to report the effect and implications of these inhibitors in industrial processes and applications. These studies will contribute to the optimisation of industrial processes by using modified enzymes not influenced by the natural inhibitors. They will also allow careful selection of raw material and reaction conditions, and future development of new genetic varieties low in inhibitors. These are all new and very promising concepts for the food and feed sector.

Highly thermostable amylase and pullulanase of the extreme thermophilic eubacterium Rhodothermus marinus: production and partial characterization

Five strains of the extreme thermophilic Rhodothermus marinus were screened for the production of amylolytic and pullulytic activities. The culture medium for the selected strain, R. marinus ITI 990, was optimized using central composite designs for enhanced enzyme production. The optimized medium containing 1.5 gl(-1) of maltose and 8.3 gl(-1) of yeast extract yielded amylase, pullulanase and alpha-glucosidase activities of 45, 33 and 2.1 nkatml(-1), respectively. Among the various carbon sources tested, maltose was most effective for the formation of these enzymes, followed by soluble maize starch, glycogen and pullulan. The crude amylase and pullulanase showed maximum activities at pH 6.5-7.0, and 85 and 80 degrees C, respectively. At 85 degrees C amylase and pullulanase had half lives of 3 h and 30 min, respectively.

Enhanced secretion and low temperature stabilization of a hyperthermostable and Ca2+-independent alpha-amylase of Geobacillus thermoleovorans by surfactants

AIMS

Selection of suitable surfactants for enhancing and stabilizing alpha-amylase of Geobacillus thermoleovorans.

METHODS AND RESULTS

Geobacillus thermoleovorans was cultivated in shake flasks containing 50 ml of starch-yeast extract-tryptone (SYT) medium with/without surfactants. Titres of the enzyme in media were monitored. The enzyme was also preserved at 4 degrees C with/without surfactants and enzyme activities were determined. Among polyethylene glycol (PEGs) of different molecular weights, PEG 8000 (0.5%, w/v) caused a slight increase in the enzyme titre, while Tween-20, Tween-40 and Tween-60 (0.03%, w/v) exerted a significant stimulatory effect on enzyme secretion. In the presence of SDS, Tween-80 and cholic acid (0.03%, w/v), the enzyme production was nearly twofold higher than that in the control. The anionic (SDS, cholic acid) and non-ionic (Tweens) detergents increased the cell membrane permeability, and thus, enhanced alpha-amylase secretion. Furthermore, anionic surfactants exhibited stabilizing effect on the enzyme during preservation at 4 degrees C.

CONCLUSIONS

PEG 8000 and the ionic detergents (SDS, cholic acid and Tween-80) were more effective in the solubilization of cell membrane components, and enhancing enzyme yields than the cationic detergents such as CTAB (N,Cetyl-N,N,N-trimethyl ammonium bromide). Further, these surfactants were found to stabilize the enzyme at 4 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

The secretion of Ca2+-independent hyperthermostable alpha-amylase was enhanced in the presence of certain anionic and non-ionic detergents in the medium. Furthermore, the surfactants stabilized the enzyme during preservation at 4 degrees C. The use of this enzyme in starch hydrolysis eliminates the addition of Ca2+ in starch liquefaction and its subsequent removal by ion exchange from sugar syrups.

Phage display selects for amylases with improved low pH starch-binding

Directed evolution of secreted industrial enzymes is hampered by the lack of powerful selection techniques. We have explored surface display to select for enzyme variants with improved binding performance on complex polymeric substrates. By a combination of saturation mutagenesis and phage display we selected alpha-amylase variants, which have the ability to bind starch substrate at industrially preferred low pH conditions. First we displayed active alpha-amylase on the surface of phage fd. Secondly we developed a selection system that is based on the ability of alpha-amylase displaying phages to bind to cross-linked starch. This system was used to probe the involvement of specific beta-strands in substrate interaction. Finally, a saturated library of alpha-amylase mutants with one or more amino acid residues changed in their Cbeta4 starch-binding domain was subjected to phage display selection. Mutant molecules with good starch-binding and hydrolytic capacity could be isolated from the phage library by repeated binding and elution of phage particles at lowered pH value. Apart from the wild type alpha-amylase a specific subset of variants, with only changes in three out of the seven possible positions, was selected. All selected variants could hydrolyse starch and heptamaltose at low pH. Interestingly, variants were found with a starch hydrolysis ratio at pH 4.5/7.5 that is improved relative to the wild type alpha-amylase. These data demonstrate that useful alpha-amylase mutants can be selected via surface display on the basis of their binding properties to starch at lowered pH values.