Characterization of a phosphotriesterase from genetically-engineered Escherichia coli

Environmental Decontamination of a Chemical Warfare Simulant Utilizing a Membrane Vesicle-Encapsulated Phosphotriesterase

While technologies for the remediation of chemical contaminants continue to emerge, growing interest in green technologies has led researchers to explore natural catalytic mechanisms derived from microbial species. One such method, enzymatic degradation, offers an alternative to harsh chemical catalysts and resins. Recombinant enzymes, however, are often too labile or show limited activity when challenged with nonideal environmental conditions that may vary in salinity, pH, or other physical properties. Here, we demonstrate how phosphotriesterase encapsulated in a bacterial outer membrane vesicle can be used to degrade the organophosphate chemical warfare agent (CWA) simulant paraoxon in environmental water samples. We also carried out remediation assays on solid surfaces, including glass, painted metal, and fabric, that were selected as representative materials, which could potentially be contaminated with a CWA.

Cell surface display of organophosphorus hydrolase for sensitive spectrophotometric detection of p-nitrophenol substituted organophosphates

Organophosphates (OPs) widely exist in ecosystem as toxic substances, for which sensitive and rapid analytical methods are highly requested. In the present work, by using N-terminal of ice nucleation protein (INP) as anchoring motif, a genetically engineered Escherichia coli (E. coli) strain surface displayed mutant organophosphorus hydrolase (OPH) (S5) with improved enzyme activity was successfully constructed. The surface location of INP-OPH fusion was confirmed by SDS-PAGE analysis and enzyme activity assays. The OPH-displayed bacteria facilitate the hydrolysis of p-nitrophenol (PNP) substituted organophosphates to generate PNP, which can be detected spectrometrically at 410 nm. Over 90% of the recombinant protein present on the surface of microbes demonstrated enhanced enzyme activity and long-term stability. The OPH activity of whole cells was 2.16 U/OD₆₀₀ using paraoxon as its substrate, which is the highest value reported so far. The optimal temperature for OPH activity was around 55 °C, and suspended cultures retained almost 100% of its activity over a period of one month at room temperature, exhibiting the better stability than free OPH. The recombinant E. coli strain could be employed as a whole-cell biocatalyst for detecting PNP substituted OPs at wider ranges and lower detection limits. Specifically, the linear ranges of the calibration curves were 0.5-150 μM paraoxon, 1-200 μM parathion and 2.5-200 μM methyl parathion, and limits of detection were 0.2 μM, 0.4 μM and 1 μM for paraoxon, parathion and methyl parathion, respectively (S/N=3). These results indicate that the engineered OPH strain is a promising multifunctional bacterium that could be used for further large-scale industrial and environmental applications.

Purification and characterization of phosphotriesterases from Pseudomonas aeruginosa F10B and Clavibacter michiganense subsp. insidiosum SBL11

A microbial biodegradation of monocrotophos was studied in the present investigation. The monocrotophos-degrading enzyme was purified and characterized from two soil bacterial strains. The cells were disrupted and the membrane-bound fractions were studied for purification and characterization. Solubilization of the membrane-bound fractions released nearly 80% of the bound protein. Phase separation further enriched the enzyme fraction 34-41 times. The enzyme phosphotriesterase (PTE) from both the strains was purified to more than 1000-fold with 13%-16% yield. Purified PTE from Clavibacter michiganense subsp. insidiosum SBL11 is a monomeric enzyme with a molecular mass of 43.5 kDa (pI of 7.5), while PTE from Pseudomonas aeruginosa F10B is a heterodimeric enzyme with a molecular mass of 43 and 41 kDa (pI of 7.9 and 7.35). Both purified enzymes are stable enzymes with peak activity at pH 9.0. The enzyme from strain F10B was more thermostable (half-life=7.3 h) than that from SBL11 (half-life=6.4 h at 50 degrees C), while both showed the same temperature optimum of 37 degrees C. Inhibitors like dithiothreitol and EDTA inhibited the purified enzyme, while p-chloromercuribenzoic acid and indoleacetic acid had a very little effect.