Stability of an extreme halophilic alkaline phosphatase from Halobacterium salinarium in non-conventional medium

Production and Characterization of α-Amylase from an Extremely Halophilic Archaeon, Haloferax sp. HA10

Haloarchaea are found at very high concentrations in salt-conditioned environments, hence produce enzymes which are able to catalyze reactions under harsh conditions, typical of many industrial processes. In the present study, culture conditions for extracellular amylase production from Haloarchaea isolated from a solar saltern were optimized and the purified enzyme was characterized. Haloferax sp. HA10 showed maximum amylase production at 3 M NaCl, 37 °C, pH=7 and 1% starch content. Purified α-amylase was a calcium-dependent enzyme with an estimated molecular mass of about 66 kDa and many industrially useful properties. It was found to be stable in a broad range of pH (from 5 to 9) and NaCl concentrations (from 0.5 to 3.0 M), retaining 48% activity even at 4 M. The optimal temperature for Haloferax sp. HA10 amylase activity was 55 °C (99% activity), and 57% activity was retained at 80 °C, which dropped to 44% with the increase of temperature to 90 or 100 °C. It was able to sustain various surfactants and detergents. To the best of our knowledge the detergent-stable α-amylases from halophilic archaeon have not been reported yet.

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

The effect of surfactants, both in water-in-oil microemulsions (hydrated reverse micelles) and aqueous solutions upon enzymatic processes is reviewed, with special emphasis on the effect of the surfactant upon the kinetic parameters of the process. Differences and similarities between processes taking place in aqueous and organic solvents are highlighted, and the main models currently employed to interpret the results are briefly discussed.

Lipolytic activity from Halobacteria: screening and hydrolase production

Strains of Halobacteria from an Algerian culture collection were screened for their lipolytic activity against p-nitrophenyl butyrate (PNPB) and p-nitrophenyl palmitate (PNPP). Most strains were active on both esters and 12% hydrolyzed olive oil. A strain identified as Natronococcus sp. was further studied. It grew optimally at 3.5 M NaCl, pH 8 and 40 degrees C. An increase in temperature shifted the optimum salt concentration range for growth from a wider range of 2-4 M, obtained at 25-30 degrees C, to a narrower range of 3.5-4 M, obtained at 35-40 degrees C. At 45 degrees C the optimum salt concentration was 2 M. These results show a clear correlation between salt and temperature requirement. The optimum conditions for the production of hydrolytic activity during growth were: 3.5 M NaCl and pH 8 for PNPB hydrolytic activity and 4 M NaCl and pH 7.5 for PNPP hydrolytic activity; both at 40 degrees C. The clear supernatant of cells grown at 4 M NaCl showed olive oil hydrolysis activity (in presence of 4 M NaCl) demonstrating the occurrence of a lipase activity in this strain. To our knowledge, this is the first report of a lipase activity at such high salt concentration.

Alpha-amylase activity from the halophilic archaeon Haloferax mediterranei

The halophilic archaeon Haloferax mediterranei is able to grow in a minimal medium containing ammonium acetate as a carbon and nitrogen source. When this medium is enriched with starch, alpha-amylase activity is excreted to the medium in low concentration. Here we report methods to concentrate and purify the enzyme. The relative molecular mass of the enzyme, determined by gel filtration, is 50 +/- 4 kDa, and on SDS-PAGE analysis a single band appeared at 58 kDa. These results indicated that the halophilic alpha-amylase is a monomeric enzyme. The enzyme showed a salt requirement for both stability and activity, being stable from 2 to 4 M NaCl, with maximal activity at 3 M NaCl. The enzyme displayed maximal activity at pHs from 7 to 8, and its optimal temperature was in a range from 50 degrees C to 60 degrees C. The results also implicated several prototropic groups in the catalytic reaction.

Reverse micelles in organic solvents: a medium for the biotechnological use of extreme halophilic enzymes at low salt concentration

Alkaline p-nitrophenylphosphate phosphatase (pNPPase) from the halophilic archaeobacterium Halobacterium salinarum (previously halobium) was solubilized at low salt concentration in reverse micelles of hexadecyltrimethyl-ammoniumbromide in cyclohexane with 1-butanol as co-surfactant. The enzyme maintained its catalytic properties under these conditions. The thermodynamic "solvation-stabilization hypothesis" has been used to explain the bell-shaped dependence of pNPPase activity on the water content of reverse micelles, in terms of protein-solvent interactions. According to this model, the stability of the folded protein depends on a network of hydrated ions associated with acidic residues at the protein surface. At low salt concentration and low water content (the ratio of water concentration to surfactant concentration; w0), the network of hydrated ions within the reverse micelles may involve the cationic heads of the surfactant. The bell-shaped profile of the relationship between enzyme activity and w0 varied depending on the concentrations of NaCl and Mn2+.

Extreme halophilic enzymes in organic solvents

The use of halophilic extremozymes in organic media has been limited by the lack of enzymological studies in these media. To explore the behaviour of these extremozymes in organic media, different approaches have been adopted, including the dispersal of the lyophilised enzyme or the use of reverse micelles. The use of reverse micelles in maintaining high activities of halophilic extremozymes under unfavourable conditions could open new fields of application such as the use of these enzymes as biocatalysts in organic media.

Mechanism of adaptation of an atypical alkaline p-nitrophenyl phosphatase from the archaeon Halobacterium salinarum at low-water environments

Enzymes suspended in organic solvents represent a versatile system for studying the involvement of water in catalytic properties and their flexibility in adapting to different environmental conditions. The extremely halophilic alkaline p-nitrophenylphosphate phosphatase from the archaeon Halobacterium salinarum was solubilized in an organic medium consisting of reversed micelles of hexadecyltrimethylammoniumbromide in cyclohexane, with 1-butanol as cosurfactant. Hydrolysis of p-nitrophenylphosphate was nonlinear with time when the enzyme was microinjected into reversed micelles that contained substrate. These data are consistent with a kinetic model in which the enzyme is irreversibly converted from an initial form to a final stable form during the first seconds of the encapsulation process. The model features a rate constant (k) for that transition and separate hydrolysis rates, v(1) and v(2), for the two forms of the enzyme. The enzyme conversion may be governed by the encapsulation process.

An extreme halophilic enzyme active at low salt in reversed micelles

Possible biotechnological applications of extreme halophilic enzymes are strongly determined by their high salt requirement of around 4 M NaCl. Consequently, the use of these in organic media seemed to be unlikely. However, we have succeeded in dissolving a halophilic enzyme, p-nitrophenylphosphate phosphatase from the archaeon Halobacterium salinarum, in an organic medium by creating a reverse micellar system with very low salt concentration. The enzyme retained its catalytic properties in reversed micelles made with an anionic surfactant (dioctyl sodium sulphosuccinate) or with a cationic surfactant (hexadecyltrimethylammonium bromide) in cyclohexane plus 1-butanol as co-surfactant. The dependence of the rate of hydrolysis of p-nitrophenylphosphate phosphate on the molar water/surfactant ratio (w(0) value) showed a bell-shaped curve for each surfactant system. Kinetic parameters were determined in each system. The enzymatic reaction appeared to follow Michaelis-Menten kinetics with the anionic surfactant only. The kinetic behaviour was determined at different concentrations of Mn(2+) in reversed micelles of dioctyl sodium sulphosuccinate as surfactant.