Detoxification of the organophosphate nerve agent coumaphos using organophosphorus hydrolase immobilized on cellulose materials

Coupling Peptide-Based Encapsulation of Enzymes with Bacteria for Paraoxon Bioremediation

The catalytic efficiency of enzymes can be harnessed as an environmentally friendly solution for decontaminating various xenobiotics and toxins. However, for some xenobiotics, several enzymatic steps are needed to obtain nontoxic products. Another challenge is the low durability and stability of many native enzymes in their purified form. Herein, we coupled peptide-based encapsulation of bacterial phosphotriesterase with soil-originated bacteria, Arthrobacter sp. 4Hβ as an efficient system capable of biodegradation of paraoxon, a neurotoxin pesticide. Specifically, recombinantly expressed and purified methyl parathion hydrolase (MPH), with high hydrolytic activity toward paraoxon, was encapsulated within peptide nanofibrils, resulting in increased shelf life and retaining ∼50% activity after 132 days since purification. Next, the addition of Arthrobacter sp. 4Hβ, capable of degrading para-nitrophenol (PNP), the hydrolysis product of paraoxon, which is still toxic, resulted in nondetectable levels of PNP. These results present an efficient one-pot system that can be further developed as an environmentally friendly solution, coupling purified enzymes and native bacteria, for pesticide bioremediation. We further suggest that this system can be tailored for different xenobiotics by encapsulating the rate-limiting key enzymes followed by their combination with environmental bacteria that can use the enzymatic step products for full degradation without the need to engineer synthetic bacteria.

Bioremediation and bioscavenging for elimination of organophosphorus threats: An approach using enzymatic advancements

Organophosphorus compounds (OP) are highly toxic pesticides and nerve agents widely used in agriculture and chemical warfare. The extensive use of these chemicals has severe environmental implications, such as contamination of soil, water bodies, and food chains, thus endangering ecosystems and biodiversity. Plants absorb pesticide residues, which then enter the food chain and accumulate in the body fat of both humans and animals. Numerous human cases of OP poisoning have been linked to both acute and long-term exposure to these toxic OP compounds. These compounds inhibit the action of the acetylcholinesterase enzyme (AChE) by phosphorylation, which prevents the breakdown of acetylcholine (ACh) neurotransmitter into choline and acetate. Thus, it becomes vital to cleanse the environment from these chemicals utilizing various physical, chemical, and biological methods. Biological methods encompassing bioremediation using immobilized microbes and enzymes have emerged as environment-friendly and cost-effective approaches for pesticide removal. Cell/enzyme immobilized systems offer higher stability, reusability, and ease of product recovery, making them ideal tools for OP bioremediation. Interestingly, enzymatic bioscavengers (stoichiometric, pseudo-catalytic, and catalytic) play a vital role in detoxifying pesticides from the human body. Catalytic bioscavenging enzymes such as Organophosphate Hydrolase, Organophosphorus acid anhydrolase, and Paraoxonase 1 show high degradation efficiency within the animal body as well as in the environment. Moreover, these enzymes can also be employed to decontaminate pesticides from food, ensuring food safety and thus minimizing human exposure. This review aims to provide insights to potential collaborators in research organizations, government bodies, and industries to bring advancements in the field of bioremediation and bioscavenging technologies for the mitigation of OP-induced health hazards.

A Microbial Electrochemical Technology to Detect and Degrade Organophosphate Pesticides

Organophosphate (OP) pesticides cause hundreds of illnesses and deaths annually. Unfortunately, exposures are often detected by monitoring degradation products in blood and urine, with few effective methods for detection and remediation at the point of dispersal. We have developed an innovative strategy to remediate these compounds: an engineered microbial technology for the targeted detection and destruction of OP pesticides. This system is based upon microbial electrochemistry using two engineered strains. The strains are combined such that the first microbe (E. coli) degrades the pesticide, while the second (S. oneidensis) generates current in response to the degradation product without requiring external electrochemical stimulus or labels. This cellular technology is unique in that the E. coli serves only as an inert scaffold for enzymes to degrade OPs, circumventing a fundamental requirement of coculture design: maintaining the viability of two microbial strains simultaneously. With this platform, we can detect OP degradation products at submicromolar levels, outperforming reported colorimetric and fluorescence sensors. Importantly, this approach affords a modular, adaptable strategy that can be expanded to additional environmental contaminants.

Prolidase - A protein with many faces

Prolidase is a metal-dependent peptidase specialized in the cleavage of dipeptides containing proline or hydroxyproline on their C-termini. Prolidase homologues are found in all kingdoms of life. The importance of prolidase in human health is underlined by a rare hereditary syndrome referred to as Prolidase Deficiency. A growing number of studies highlight the importance of prolidase in various other human conditions, including cancer. Some recent studies link prolidase's activity-independent regulatory role to tumorigenesis. Furthermore, the enzyme or engineered variants have some applications in biotechnology. In this short review, we aim to highlight different aspects of the protein the importance of which is increasingly recognized over the last years.

Biocatalytic membrane reactor development for organophosphates degradation

Organophosphates (OPs) are highly toxic compounds used as pesticides and nerve agents. The devastating effects, reported in different studies, on the environment and human health indicate a serious scenario for both instantaneous and long terms effects. Bio-based strategies for OPs degradation seem the most promising solutions, particularly when extremophiles enzymes are used. These systems permit OPs degradation with high efficiency and specificity under mild conditions. However, as frequently observed, enzymes can easily lose activity in batch systems, so that a strategy to improve biocatalyst stability is highly needed, in order to develop continuous systems. In this work, for the first time, a continuous biocatalytic system for organophosphates (OPs) detoxification has been proposed by using a triple mutant of the thermostable phosphotriesterase (named SsoPox) isolated from the hyperthermophilic archaeon Sulfolobus solfataricus. The enzyme was covalently immobilized on polymeric membranes to develop a biocatalytic membrane reactor (BMR) able to hydrolyse a pesticide (paraoxon) contained in water. High paraoxon degradation (about 90%) and long term stability (1 year) were obtained when the enzyme was covalently immobilized on hydrophilic membranes. On the contrary, the enzyme in batch system completely loses its activity within few months after its solubilisation in buffer.

Enzymatic detoxification of organophosphorus pesticides and related toxicants

Millions of cases of pesticide intoxication occur yearly and represent a public health problem. In addition, pesticide poisoning is the preferred suicidal method in rural areas. The use of enzymes for the treatment of intoxication due to organophosphorus pesticides was proposed decades ago. Several enzymes are able to transform organophosphorus compounds such as pesticides and nerve agents. Some specific enzymatic treatments have been proposed, including direct enzyme injection, liposome and erythrocytes carriers, PEGylated preparations and extracorporeal enzymatic treatments. Nevertheless, no enzymatic treatments are currently available. In this work, the use of enzymes for treating of organophosphorus pesticide intoxication is critically reviewed and the remaining challenges are discussed.

Optimization of the Use of His₆-OPH-Based Enzymatic Biocatalysts for the Destruction of Chlorpyrifos in Soil

Applying enzymatic biocatalysts based on hexahistidine-containing organophosphorus hydrolase (His₆-OPH) is suggested for the decomposition of chlorpyrifos, which is actively used in agriculture in many countries. The application conditions were optimized and the following techniques was suggested to ensure the highest efficiency of the enzyme: first, the soil is alkalinized with hydrated calcitic lime Ca(OH)₂, then the enzyme is introduced into the soil at a concentration of 1000 U/kg soil. Non-equilibrium low temperature plasma (NELTP)-modified zeolite is used for immobilization of the relatively inexpensive polyelectrolyte complexes containing the enzyme His₆-OPH and a polyanionic polymer: poly-l-glutamic acid (PLE₅₀) or poly-l-aspartic acid (PLD₅₀). The soil’s humidity is then increased up to 60–80%, the top layer (10–30 cm) of soil is thoroughly stirred, and then exposed for 48–72 h. The suggested approach ensures 100% destruction of the pesticide within 72 h in soils containing as much as 100 mg/kg of chlorpyrifos. It was concluded that using this type of His₆-OPH-based enzyme chemical can be the best approach for soils with relatively low humus concentrations, such as sandy and loam-sandy chestnut soils, as well as types of soil with increased alkalinity (pH 8.0–8.4). Such soils are often encountered in desert, desert-steppe, foothills, and subtropical regions where chlorpyrifos is actively used.

[Decontamination of organophosphorus compounds: Towards new alternatives]

Organophosphorus coumpounds (OP) are toxic chemicals mainly used for agricultural purpose such as insecticides and were also developed and used as warfare nerve agents. OP are inhibitors of acetylcholinesterase, a key enzyme involved in the regulation of the central nervous system. Chemical, physical and biological approaches have been considered to decontaminate OP. This review summarizes the current and emerging strategies that are investigated to tackle this issue with a special emphasis on enzymatic remediation methods. During the last decade, many studies have been dedicated to the development of biocatalysts for OP removal. Among these, recent reports have pointed out the promising enzyme SsoPox isolated from the archaea Sulfolobus solfataricus. Considering both its intrinsic stability and activity, this hyperthermostable enzyme is highly appealing for the decontamination of OP.

Complex Coacervate Core Micelles for the Dispersion and Stabilization of Organophosphate Hydrolase in Organic Solvents

Organophosphate (OP) nerve agents are a class of chemical warfare agents (CWAs) that exist as bulk stocks in current and past war zones. Thus, a technology that can perform on-site decontamination in a safe and timely fashion is desirable. Here, complex coacervate core micelles (C3Ms) were used to encapsulate organophosphate hydrolase (OPH) and chemostabilize it to maintain activity after exposure to organophosphate simulants ethanol and dimethyl methylphosphonate (DMMP). C3Ms were formed by two polymers-poly(acrylic acid) (PAA) and poly(oligo(ethylene glycol) methacrylate)-b-poly(4-vinyl N-methylpyridyl iodide), (POEGMA-b-qP4VP). Complexes of the coacervate micelles with the enzyme OPH were investigated by small angle neutron scattering (SANS), dynamic light scattering (DLS), and transmission electron microscopy (TEM), demonstrating the formation of micellar structures in solution. The activity of OPH against methyl paraoxon in these C3Ms under aqueous conditions was assayed after heat treatment for 3 days at 37 °C. The OPH in C3Ms retained 88 ± 7% of its initial activity, as compared to the 48 ± 3% activity retained by OPH alone, indicating that the C3Ms were able to stabilize the enzyme to heat treatment. C3Ms transferred into the two organic solvents formed larger structures than inverse micelles formed by the block copolymer alone. The addition of OPH to the C3Ms in organic solvents did not significantly change their structure. The activity of OPH (again, against methyl paraoxon) after 24 h of incubation at 4 °C was measured and compared to that of OPH in C3Ms. While OPH alone retained less than 5% of its activity after this incubation in both solvents, OPH in C3Ms retained 35 ± 3% of its activity in DMMP and 26 ± 1% of its activity in ethanol.

Use of Ca-alginate immobilized Pseudomonas aeruginosa for repeated batch and continuous degradation of Endosulfan

The current investigation is taken up with the aim of studying repeated batch and continuous degradation of Endosulfan, using Ca-alginate immobilized cells of Pseudomonas aeruginosa isolated from an agricultural soil. The work involves the study of genes and enzymes involved in the degradation of the pesticide and was carried out with an objective of reducing the toxicity of Endosulfan by degrading it to less toxic metabolites. The long-term stability of Endosulfan degradation was studied during its repeated batch degradation, carried out over a period of 35 days. Immobilized cells of Ps. aeruginosa were able to show 60 % degradation of Endosulfan at the end of the 35th cycle with a cell leakage of 642 × 10⁴ Cfu/mL. During continuous treatment, with 2 % concentration of Endosulfan, 100 % degradation was recorded up to 100 mL/h flow rate and with 10 % concentration of the Endosulfan, and 100 and 85 % degradation was recorded at 20 mL/h flow rate and 100 mL/h flow rate, respectively. After degradation of Endosulfan, products were extracted from a large amount of spent medium using two volumes of ethyl acetate and subjected to the LC–MS analysis. Endosulfan lactone and Endosulfan ether were the products of degradation detected by the LCMS analysis. Plasmid curing experiments indicated that genes responsible for the degradation of Endosulfan are present on the chromosome and not on the plasmid, as growth of Ps. aeruginosa was observed on modified non-sulfur medium with Endosulfan after the plasmid was cured with ethidium bromide. The results of PCR indicated that there is no amplified product of ~1350 bp expected for esd gene, in Ps. aeruginosa, although there were some non-specific bands. Enzymatic degradation studies indicated that the enzymes involved in the degradation of Endosulfan are intracellular. With this investigation, it was indicated that immobilized cells of Ps.aeruginosa have the potential to be used in the bioremediation of water contaminated with Endosulfan.

Current and emerging strategies for organophosphate decontamination: special focus on hyperstable enzymes

Organophosphorus chemicals are highly toxic molecules mainly used as pesticides. Some of them are banned warfare nerve agents. These compounds are covalent inhibitors of acetylcholinesterase, a key enzyme in central and peripheral nervous systems. Numerous approaches, including chemical, physical, and biological decontamination, have been considered for developing decontamination methods against organophosphates (OPs). This work is an overview of both validated and emerging strategies for the protection against OP pollution with special attention to the use of decontaminating enzymes. Considerable efforts have been dedicated during the past decades to the development of efficient OP degrading biocatalysts. Among these, the promising biocatalyst SsoPox isolated from the archaeon Sulfolobus solfataricus is emphasized in the light of recently published results. This hyperthermostable enzyme appears to be particularly attractive for external decontamination purposes with regard to both its catalytic and stability properties.

Repeated batch and continuous degradation of chlorpyrifos by Pseudomonas putida

The present study was undertaken with the objective of studying repeated batch and continuous degradation of chlorpyrifos (O,O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate) using Ca-alginate immobilized cells of Pseudomonas putida isolated from an agricultural soil, and to study the genes and enzymes involved in degradation. The study was carried out to reduce the toxicity of chlorpyrifos by degrading it to less toxic metabolites. Long-term stability of pesticide degradation was studied during repeated batch degradation of chlorpyrifos, which was carried out over a period of 50 days. Immobilized cells were able to show 65% degradation of chlorpyrifos at the end of the 50th cycle with a cell leakage of 112 × 10(3) cfu mL(-1). During continuous treatment, 100% degradation was observed at 100 mL h(-1) flow rate with 2% chlorpyrifos, and with 10% concentration of chlorpyrifos 98% and 80% degradation was recorded at 20 mL h(-1) and 100 mL h(-1) flow rate respectively. The products of degradation detected by liquid chromatography-mass spectrometry analysis were 3,5,6-trichloro-2-pyridinol and chlorpyrifos oxon. Plasmid curing experiments with ethidium bromide indicated that genes responsible for the degradation of chlorpyrifos are present on the chromosome and not on the plasmid. The results of Polymerase chain reaction indicate that a ~890-bp product expected for mpd gene was present in Ps. putida. Enzymatic degradation studies indicated that the enzymes involved in the degradation of chlorpyrifos are membrane-bound. The study indicates that immobilized cells of Ps. putida have the potential to be used in bioremediation of water contaminated with chlorpyrifos.

Enhanced activity and stability of organophosphorus hydrolase via interaction with an amphiphilic polymer

A simple approach to enhancing the activity and stability of organophosphorus hydrolase (OPH) is developed based on interactions between the hydrophobic poly(propylene oxide) (PPO) block of amphiphilic Pluronics and the enzyme. This strategy provides an efficient route to new formulations for decontaminating organophosphate neurotoxins.

Ormosil gels doped with engineered catechol 1,2 dioxygenases for chlorocatechol bioremediation

Enzymes entrapped in wet, nanoporous silica gel have great potential as bioreactors for bioremediation because of their improved thermal, chemical, and mechanical stability with respect to enzymes in solution. The B isozyme of catechol 1,2 dioxygenase from Acinetobacter radioresistens and its mutants of Leu69 and Ala72, designed for an increased reactivity toward the environmental pollutant chlorocatechols, were encapsulated using alkoxysilanes and alkyl alkoxysilanes as precursors in varying proportions. Encapsulation of the mutants in a hydrophobic tetramethoxysilane/dimethoxydimethylsilane-based matrix yielded a remarkable 10- to 12-fold enhancement in reactivity toward chlorocatechols. These gels also showed a fivefold increase in relative reactivity toward chlorocatechols with respect to the natural substrate catechol, thus compensating for their relatively low activity for these substrates in solution. The encapsulated enzyme, unlike the enzyme in solution, proved resilient in assays carried out in urban wastewater and bacteria-contaminated solutions mimicking environmentally relevant conditions. Overall, the combination of a structure-based rational design of enzyme mutants, and the selection of a suitable encapsulation material, proved to be a powerful approach for the production and optimization of a potential bioremediation device, with increased activity and resistance toward bacterial degradation.

Biocatalytic carbon nanotube paper: a ‘one-pot’ route for fabrication of enzyme-immobilized membranes for organophosphate bioremediation

A generic methodology for a rapid and direct fabrication of enzymatically-active carbon nanotubes (CNTs) paper for organophosphates bioremediation is presented. The enzyme organophosphate hydrolase is immobilized onto CNTs simultaneously to membrane formation process.

Spectroscopic and mechanistic studies of dinuclear metallohydrolases and their biomimetic complexes

An enhanced understanding of the metal ion binding and active site structural features of phosphoesterases such as the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ), and the organophosphate degrading agent from Agrobacterium radiobacter (OpdA) have important consequences for potential applications. Coupled with investigations of the metalloenzymes, programs of study to synthesise and characterise model complexes based on these metalloenzymes can add to our understanding of structure and function of the enzymes themselves. This review summarises some of our work and illustrates the significance and contributions of model studies to knowledge in the area.

Organophosphorus acid anhydrolase from Alteromonas macleodii: structural study and functional relationship to prolidases

The bacterial enzyme organophosphorus acid anhydrolase (OPAA) is able to catalyze the hydrolysis of both proline dipeptides (Xaa-Pro) and several types of organophosphate (OP) compounds. The full three-dimensional structure of the manganese-dependent OPAA enzyme is presented for the first time. This enzyme, which was originally isolated from the marine bacterium Alteromonas macleodii, was prepared recombinantly in Escherichia coli. The crystal structure was determined at 1.8 Å resolution in space group C2, with unit-cell parameters a = 133.8, b = 49.2, c = 97.3 Å, β = 125.0°. The enzyme forms dimers and their existence in solution was confirmed by dynamic light scattering and size-exclusion chromatography. The enzyme shares the pita-bread fold of its C-terminal domain with related prolidases. The binuclear manganese centre is located in the active site within the pita-bread domain. Moreover, an Ni(2+) ion from purification was localized according to anomalous signal. This study presents the full structure of this enzyme with complete surroundings of the active site and provides a critical analysis of its relationship to prolidases.

Stabilization of organophosphorus hydrolase by entrapment in silk fibroin: formation of a robust enzymatic material suitable for surface coatings

Organophosphates are some of the most acutely toxic compounds synthesized on an industrial scale, and organophosphorus hydrolase (OPH) has the ability to hydrolyze and inactivate a number of these chemicals. However, OPH activity is vulnerable to harsh environmental conditions that would accompany its practical utility in the field; a limitation that can also be extended to conditions required for incorporation of OPH into useful materials. Here we present evidence that entrapment of OPH in silk fibroin leads to stabilization of OPH activity under a variety of conditions that would otherwise reduce free enzyme activity, such as elevated temperature, UV light exposure and the presence of detergent. Silk fibroin entrapment of OPH also allowed for its dispersal into a polyurethane-based coating that retained organophosphate hydrolysis activity after formulation, application and drying. Together, the data presented here demonstrate the utility of silk fibroin entrapment for the protection of OPH activity under a variety of environmental conditions.

Immobilization of organophosphohydrolase OpdA from Agrobacterium radiobacter by overproduction at the surface of polyester inclusions inside engineered Escherichia coli

Organophosphorus pesticides (OP) are highly toxic and are widely used as insecticides. Bacterial organophosphohydrolases which hydrolyze a variety of OPs have been considered for the clean-up of polluted environments. This study describes the engineering of Escherichia coli towards the overproduction of the organophosphohydrolase (OpdA) from Agrobacterium radiobacter at the surface of polyester inclusions. The OpdA was N-terminally fused via a designed linker region to the C-terminus of polyester inclusion-forming enzyme PhaC of Ralstonia eutropha. The PhaC-L-OpdA fusion protein was overproduced by using the strong T7 promoter and when coexpressed with genes phaA (encoding β-ketothiolase) and phaB (encoding acetoacetyl-CoA reductase) from R. eutropha this led to formation of polyester inclusions abundantly displaying OpdA. These OpdA beads showed organophosphohydrolase activity of 1,840 U/g wet polyester beads or 4,412 U/g protein. Steady state kinetics revealed that when compared with free OpdA the k(cat) (s(-1)) of 139 of immobilized OpdA was reduced by about 16.5-fold while the K(M) (M) of 2.5 × 10(-4) was increased by 1.6-fold. The immobilized OpdA showed increased temperature stability. Moreover, the stability of OpdA immobilized to polyester beads was assessed by incubating OpdA beads at 25°C for up to 11 days and no significant loss in enzyme activity was detected. The application performance of the OpdA beads with respect to hydrolysis of OPs in contaminated environments was demonstrated in wool scour spiked with fluorescent coumaphos. This study demonstrated a new strategy toward the efficient recombinant production of immobilized organophosphohydrolase, the OpdA, suitable for bioremediation applications.

Detection of organophosphorus compounds using a molecularly imprinted photonic crystal

A label free molecularly imprinted photonic crystal (MIPC) was developed to detect the degradation product of nerve agents. Mono-dispersed poly-methyl methacrylate colloidal particles with the diameter of 280 nm were used to fabricate a closely packed colloidal crystal array (CCA), and a methyl phosphonic acid (MPA) imprinted hydrogel was prepared within the CCA using 2-hydroxyethyl-methacrylate and N-isopropylacrylamide as monomers, ethyleneglycol dimethacrylate and N, N'-methylenebisacrylamide as cross-linkers, a mixture of n-octanol and acetonitrile as porogen. The diffraction intensity of the MIPC decreased significantly upon the MPA adsorption with a limit of detection (LOD) of 10(-6) molL(-1). Furthermore, the diffraction intensity decreased and blue shifted with the increase of temperature, decreased and red shifted with the increase of ionic strength. At higher pH, the diffraction intensity increased without obvious diffraction shift. The MIPC provides an indirect path to detect nerve agents (Sarin, Soman, VX and R-VX) by monitoring the MPA released from the hydrolysis of nerve agents, with LODs of 3.5 × 10(-6) molL(-1), 2.5 × 10(-5) molL(-1), 7.5 × 10(-5) molL(-1) and 7.5 × 10(-5) molL(-1) for Sarin, Soman, VX and R-VX, respectively.

Control of protein immobilization: coupling immobilization and site-directed mutagenesis to improve biocatalyst or biosensor performance

Mutagenesis and immobilization are usually considered to be unrelated techniques with potential applications to improve protein properties. However, there are several reports showing that the use of site-directed mutagenesis to improve enzyme properties directly, but also how enzymes are immobilized on a support, can be a powerful tool to improve the properties of immobilized biomolecules for use as biosensors or biocatalysts. Standard immobilizations are not fully random processes, but the protein orientation may be difficult to alter. Initially, most efforts using this idea were addressed towards controlling the orientation of the enzyme on the immobilization support, in many cases to facilitate electron transfer from the support to the enzyme in redox biosensors. Usually, Cys residues are used to directly immobilize the protein on a support that contains disulfide groups or that is made from gold. There are also some examples using His in the target areas of the protein and using supports modified with immobilized metal chelates and other tags (e.g., using immobilized antibodies). Furthermore, site-directed mutagenesis to control immobilization is useful for improving the activity, the stability and even the selectivity of the immobilized protein, for example, via site-directed rigidification of selected areas of the protein. Initially, only Cys and disulfide supports were employed, but other supports with higher potential to give multipoint covalent attachment are being employed (e.g., glyoxyl or epoxy-disulfide supports). The advances in support design and the deeper knowledge of the mechanisms of enzyme-support interactions have permitted exploration of the possibilities of the coupled use of site-directed mutagenesis and immobilization in a new way. This paper intends to review some of the advances and possibilities that these coupled strategies permit.

Removal of two organophosphate pesticides by a bacterial consortium immobilized in alginate or tezontle

In order to remove methyl-parathion (MP) and tetrachlorvinphos (TCF), a bacterial consortium was immobilized with two supports consisting of alginate beads or stones of tezontle colonized by biofilm. Removal kinetics were recorded for suspended and immobilized consortium using a mineral salt medium supplemented with MP and TCF at 25mg/L and with 0.1% (w/v) glucose as a co-substrate. The viability of the consortium cultivated in suspension was maintained for 6 days, whereas the viability of the consortium immobilized in alginate and tezontle supports was maintained for up to 11 and 13 days, respectively. Growth was enhanced when using glucose as a co-substrate. The percentage of MP removed was significantly higher (alpha=0.05) when consortium was immobilized in alginate beads and biofilm on tezontle as compared to suspension culture.

Total degradation of fenitrothion and other organophosphorus pesticides by catalytic oxidation employing Fe-TAML peroxide activators

A Fe-TAML/H2O2 catalytic oxidation process achieves facile in-solution total degradation of fenitrothion and two other organophosphorus (OP) pesticides. Degradation products have been identified and quantified providing evidence for oxidative hydrolysis, oxidative desulfuration, perhydrolysis, and deep oxidation. Degradation pathways can be selected by pH control to completely obviate all toxic residuals. Aquatic toxicity assays support the environmental compatibility of the degradation process.

Calmodulin-mediated reversible immobilization of enzymes

This work demonstrates the use of the protein calmodulin, CaM, as an affinity tag for the reversible immobilization of enzymes on surfaces. Our strategy takes advantage of the of the reversible, calcium-mediated binding of CaM to its ligand phenothiazine and of the ability to produce fusion proteins between CaM and a variety of enzymes to reversibly immobilize enzymes in an oriented fashion to different surfaces. Specifically, we employed two different enzymes, organophosphorus hydrolase (OPH) and beta-lactamase and two different solid supports, a silica surface and cellulose membrane modified by covalently attaching a phenothiazine ligand, to demonstrate the versatility of our immobilization method. Fusion proteins between CaM-OPH and CaM-beta-lactamase were prepared by using genetic engineering strategies to introduce the calmodulin tail at the N-terminus of each of the two enzymes. In the presence of Ca(2+), CaM adopts a conformation that favors interaction between hydrophobic pockets in CaM and phenothiazine, while in the presence of a Ca(2+)-chelating agent such as EGTA, the interaction between CaM and phenothiazine is disrupted, thus allowing for removal of the CaM-fusion protein from the surface under mild conditions. CaM also acts as a spacer molecule, orienting the enzyme away from the surface and toward the solution, which minimizes enzyme interactions with the immobilization surface. Since the method is based on the highly selective binding of CaM to its phenothiazine ligand, and this is covalently immobilized on the surface, the method does not suffer from ligand leaching nor from interference from other proteins present in the cell extract. An additional advantage lies in that the support can be regenerated by passing through EGTA, and then reused for the immobilization of the same or, if desired, a different enzyme. Using a fusion protein approach for immobilization purposes avoids the use of harsh conditions in the immobilization and/or regeneration steps, which could cause inactivation of the immobilized enzyme. Moreover, we have demonstrated that the CaM affinity tag allows immobilization of enzymes on a variety of surfaces without compromising their enzymatic activity substantially; for example, the immobilized OPH retained more than 80% of the activity of the free enzyme. Our results with beta-lactamase showed the feasibility of using a phenothiazine surface in several consecutive loading and regeneration cycles. This can be advantageous when expensive and/or difficult to obtain immobilization surfaces have to be employed; the immobilization surface could be reused to immobilize the same or a different enzyme using the CaM affinity tail. We also determined that the phenothiazine-modified silica particles are stable for long periods of time, i.e., up to 2 years when stored at 4 degrees C. It is envisioned that this type of reversible immobilization may find applications in the development of reversible, reusable biosensors and bioreactors endowed with the additional advantage that the biological element at the surface of the sensor or bioreactor could be replaced under mild conditions when needed to sense or process a different target molecule.