Aqueous two-phase systems in biochemical recovery

Enrichment of reticulocytes from whole blood using aqueous multiphase systems of polymers

This paper demonstrates the enrichment of reticulocytes by centrifuging whole blood through aqueous multiphase systems (AMPSs)-immiscible phases of solutions of polymers that form step-gradients in density. The interfaces of an AMPS concentrate cells; this concentration facilitates the extraction of blood enriched for reticulocytes. AMPS enrich reticulocytes from blood from both healthy and hemochromatosis donors. Varying the osmolality and density of the phases of AMPS provides different levels of enrichment and yield of reticulocytes. A maximum enrichment of reticulocytemia of 64 ± 3% was obtained from donors with hemochromatosis. When used on peripheral blood from normal donors, AMPS can provide a higher yield of enriched reticulocytes and a higher proportion of reticulocytes expressing CD71 than differential centrifugation followed by centrifugation over Percoll. Blood enriched for reticulocytes by AMPS could be useful for research on malaria. Several species of malaria parasites show a preference to invade young erythrocytes and reticulocytes; this preference complicates in vitro cultivation of these species in human blood. Plasmodium knowlesi malaria parasites invade normal human blood enriched for reticulocytes by AMPSs at a rate 2.2 times greater (P < 0.01) than they invade unenriched blood. Parasite invasion in normal blood enriched by AMPS was 1.8 times greater (P < 0.05) than in blood enriched to a similar reticulocytemia by differential centrifugation followed by centrifugation over Percoll. The enrichment of reticulocytes that are invaded by malaria parasites demonstrates that AMPSs can provide a label-free method to enrich cells for biological research.

Molecular dynamics simulations on aqueous two-phase systems - Single PEG-molecules in solution

Background

Molecular Dynamics (MD) simulations are a promising tool to generate molecular understanding of processes related to the purification of proteins. Polyethylene glycols (PEG) of various length are commonly used in the production and purification of proteins. The molecular mechanisms behind PEG driven precipitation, aqueous two-phase formation or the effects of PEGylation are however still poorly understood.

Results

In this paper, we ran MD simulations of single PEG molecules of variable length in explicitly simulated water. The resulting structures are in good agreement with experimentally determined 3D structures of PEG. The increase in surface hydrophobicity of PEG of longer chain length could be explained on an atomic scale. PEG-water interactions as well as aqueous two-phase formation in the presence of PO₄ were found to be correlated to PEG surface hydrophobicity.

Conclusions

We were able to show that the taken MD simulation approach is capable of generating both structural data as well as molecule descriptors in agreement with experimental data. Thus, we are confident of having a good in silico representation of PEG.

Interfacial tension in phase-separated aqueous cationic/anionic surfactant mixtures

Interfacial tensions in two aqueous phase-separated cationic/anionic surfactant mixtures, CTAB/AS and 12-3-12/AS, without and with NaBr added were determined by the spinning drop method at 318.15 K. CTAB, 12-3-12 and AS are the abbreviations for cetyltrimethylammonium bromide, 1,3-propanediyl-bis(dodecyldimethylammonium bromide) and sodium dodecyl sulfonate, respectively. The interfacial tension sigma was found to be in the range of 0.06-21 microNm(-1). Toward a better understanding of the influence of the concentration difference between the separated phases in aqueous two-phase systems (ATPS) to interfacial tension, compositions of equilibrium phases were determined by elemental analysis coupled with material balance and electroneutrality. The investigation indicates that the concentration differences of surfactant ions between the separated phases and the adsorption of surfactant ions at the interface are the decisive factors determining the magnitude of interfacial tension.

Interfacial Tension in Phase-Separated Gelatin/Dextran Aqueous Mixtures

The effect of solute concentrations on interfacial tension was investigated in phase-separated mixtures of dextran and gelatin over a range of concentrations that covered different tie-lines and different positions on one tie-line. The investigations were carried out using equilibrated gelatin-rich and dextran-rich phases in a computer-controlled Couette device at 40 degrees C (above the gelation point of gelatin) and interfacial tensions were measured using the retracting drop method. The results show that the interfacial tension can be related to the length of the tie-line or to the difference in the concentration of dextran (or gelatin) in the separated phases. Interfacial tension increases as either of these parameters increases. For concentrations lying on any single tie-line, the interfacial tension is constant and independent of the concentration of biopolymers. Also, the addition of small amounts of low molecular weight dextran to a dextran-rich phase does not significantly affect the interfacial tension between the gelatine-rich and dextran-rich phases. Experimental results were also compared with theoretical predictions of the interfacial tension using a Flory-Huggins based analysis of the measured tie-line data. Reasonable agreement was found between predicted and measured values, indicating that this approach captures the basic physics of the system.

Simultaneous biosynthesis and purification of two extracellular Bacillus hydrolases in aqueous two-phase systems

Thermostable alpha-amylase with temperature optimum at 80 degrees C, molecular mass 58 kDa and pI point 6.9 was purified from a catabolite resistant Bacillus licheniformis strain. The enzyme was sensitive to inhibition by metal ions and N-bromosuccinimide. The partition behaviour of this enzyme in aqueous two-phase systems (ATPS) of the polymer-polymer-water type was investigated and some effects of type, molecular weight and concentration of phase components were studied. Up to 100% retention in the bottom phase of polyethylene glycol 10,000-20,000/dextran 200 system was reached. Best partition conditions were obtained in PEG 10,000-20,000/polyvinyl alcohol 200 systems, where the partition coefficient K increased 750 times to 7.5. Simultaneous production and purification of alpha-amylase and serine proteinase in PEG-polymer-water ATPS were examined. In the system PEG 6,000/ficoll, up to 90% of the amylase was retained in the bottom phase, whereas about 95% of the total protein (K = 22.8) and 60-75% of the proteinase were in the top phase. Similar separation of the enzymes from laboratory supernatant was obtained in system PEG/Na2SO4.

Investigation of aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process

In efforts to apply a polymer-based aqueous biphasic system (ABS) extraction to the paper pulping process, the study of the distribution of various lignin and cellulosic fractions in ABS and the effects of temperature on system composition and solute partitioning have been investigated. The partitioning of three lignin species (Indulin AT, Indulin C, and Reax 85A) have been studied in ABS prepared from stock solutions of 40% (w/w) poly(ethylene glycol) (PEG)-2000 and increasing concentrations of K2CO3, (NH4)2SO4, and NaOH. The partitioning of these lignins is affected by the free energy of hydration of the salt forming the ABS, the tie line length, and the dissociation of the sulfonic acid and hydroxyl groups of the distributed solutes. The partitioning of fibrous cellulose and diethylaminoethyl cellulose have been studied in 40% (w/w) PEG-2000-(NH4)2SO4 ABS. The hydrophilic nature of these species is important in terms of their phase preference when designing a polymer-based aqueous biphasic extraction process for use in a paper pulping process. Both cellulosic samples do not dissolve, but rather report to the salt-rich phase of an ABS. In both chemical pulping and Organosolv pulping, temperatures in excess of 120 degrees C are needed to solubilize the lignin from the cellulose fraction of wood. To study the effects of temperature on the phase diagram and solute partitioning, phthalic acid and NH499TcO4 (as system probes) have been partitioned in 40% (w/w) PEG-2000-(NH4)2SO4 ABS at known tie line lengths as a function of temperature. Temperature does not appear to affect the partitioning results beyond the expected increase in phase divergence as temperature is increased. The PEG-2000 polymer itself appears to be stable to chemical pulping conditions.

Extractive cultivation of recombinant Escherichia coli using aqueous two phase systems for production and separation of extracellular xylanase

Recombinant Escherichia coli (pATBX 1.8) secreting extracellular xylanase was used as a model system to study the application of an aqueous two phase system for extractive cultivation. An increase in the polymer concentrations from 6 to 20% in the polyethylene glycol phosphate aqueous two phase system resulted in an increase in the phase volume ratio with a concomitant decrease in the partition coefficient (K) and recovery of xylanase in the top phase. However, varying phosphate concentrations from 8 to 16% decreased both the phase volume ratio and the partition coefficient of xylanase. The polyethylene glycol (6%) and phosphate (12%) system was found to be optimum for extracellular cultivation of E. coli, where extracellular xylanase was selectively partitioned to the top phase giving a purification ratio of above 1.0. The process was extended to a semicontinuous operating mode at the optimal condition, wherein the top phase containing xylanase was recovered and the surviving cells were recycled together with the new top phase. The maximum recovery of xylanase was obtained after 12 h in the top phase with a twofold increase in the specific activity as compared to the one obtained in the reference fermentation. In the present work, we report for the first time the use of the two phase system for the extractive cultivation of recombinant E. coli (pATBX 1.8) with the purpose of obtaining a simple and inexpensive separation procedure and achieving the maximal extraction of xylanase to one phase.

Partitioning of small organic molecules in aqueous biphasic systems

Aqueous biphasic systems (ABS) are suitable for the separation of small organic molecules in industrial and environmental applications and thus, it is important to correlate partitioning behavior of model organic solutes with their structure in order to develop predictive models. The partitioning behavior of five, uncharged, substituted benzenes (benzene, toluene. chlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene) were studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts (K3PO4, K2CO3, (NH4)2SO4 and NaOH). For a given solute and a defined concentration of salt, the partition coefficients increase as the deltaGhyd value of the salt anion becomes more negative (e.g., Dbenzene increases in the order OH- <SO42- <CO32- <PO43-). In a given salt, the distribution ratios increase in the order benzene<toluene<chlorobenzene< 1,4-dichlorobenzene< 1,2,4-trichlorobenzene. The partitioning behavior of the solutes in PEG-salt ABS was found to be strongly correlated with their partitioning coefficients in 1-octanol-water biphasic systems.

Separation and recovery of food coloring dyes using aqueous biphasic extraction chromatographic resins

Aqueous biphasic systems (ABS) and aqueous biphasic extraction chromatographic (ABEC) resins are currently under investigation for their utility in the removal of color from textile plant wastes. The structures of several widely used food colorings, suggest that these dyes would also be retained on the resins. In work currently in progress, we have begun to investigate the retention and resolution of several common food colorings including indigo carmine, amaranth, carminic acid. erythrosin B, tartrazine and quinoline yellow. The relationship between the uptake of these dyes on ABEC resins in terms of the binding strengths and capacities of the resins and their partitioning behavior in ABS is illustrated. Some possible theoretical and practical approaches to the prediction of the partitioning and retention behavior is discussed.

Extractive bioconversions in aqueous two-phase systems

Although extractive bioconversions in aqueous two-phase systems (ATPSs) have been studied for over a decade, this has not yet resulted in widespread industrial application. The main reasons are the cost of the phase-forming polymers and the complexity of ATPS behavior. A number of recent developments may give a new impetus to this technology. First of all, the use of extractive bioconversions in ATPSs has recently been extended to high-value protein products, while in the meantime the development of low-cost ATPSs is ongoing. Furthermore, novel chromatographic methods enable the analysis of polymer and metabolite compositions in complex ATPS mixtures, and recently employed statistical experimental designs provide a tool for efficient data gathering, while they also reveal synergistic effects between process parameters. Together, these developments open the way towards improved modeling of partitioning behavior in ATPSs.

Protein partition between the different phases comprising poly(ethylene glycol)-salt aqueous two-phase systems, hydrophobic interaction chromatography and precipitation: a generic description in terms of salting-out effects

The solution behaviour of selected proteins has been studied under conditions promoting precipitation, binding to mildly hydrophobic adsorbents or partition. Solvophobic theory may be used to describe these forms of protein partition. The tendency of a protein to partition therein is dependent upon surface properties of the protein solute mediated by the concentration and nature of added salts. As applied to partitioning in poly(ethylene glycol) (PEG)-salt systems this implies that linear (Brönsted) relationships apply only to proteins partitioned close to the critical point. At longer tie-line lengths protein partitioning is increasingly influenced by salting-out forces. This is confirmed by the observed behaviour of the proteins. The point at which this behaviour changes has been unambiguously defined enabling the direct comparison of phase transition of proteins during partition in all systems. The results obtained show that phase transition during adsorption and partition occur at similar concentrations of salt. This is less than that required to promote precipitation. It appears, from these limited studies, that top-phase preferring proteins are partitioned at salt concentrations above those required to cause adsorption. Proteins preferring the lower phase are partitioned at salt concentrations close to or below those required for adsorption. This raises questions regarding the solvated molecular form of the partitioned proteins and the definition of the partition coefficient.

Aqueous two-phase partition of complex protein feedstocks derived from brain tissue homogenates

This study describes the application of aqueous two-phase partition using polyethylene glycol (PEG)-potassium phosphate systems for the direct recovery of proteins, and aggregates thereof, from mammalian brain tissue homogenates. Investigation of established methodologies for the purification of prion proteins (PrP) from bovine brain affected with transmissible spongiform encephalopathy (BSE) has identified an alternative purification regime based on aqueous two-phase partition. This circumvents energy-intensive and rate-limiting unit operations of ultracentrifugation conventionally used for isolation of PrP. Selectivity of various PEG-phosphate systems varied inversely with polymer molecular mass. The maximum protein recovery from bovine brain extracts was obtained with systems containing PEG 300. Manipulation of the aqueous environment, to back-extract protein product from the PEG-rich top phase into the phosphate-rich lower phase, enabled integration of ATPS with conventional hydrophobic interaction chromatography (HIC) which selectively removes obdurate contaminating proteins (i.e. ferritin).

New methods for separation and recovery of biomolecules

New methods and applications in the separation of biomolecules are reviewed, with an emphasis on the large-scale recovery of proteins. Highlights include the advent of flow-through particles in perfusion chromatography, which allows for very high flow rates, while retaining a high chromatographic efficiency.