Continuous biodegradation of parathion by immobilized Sphingomonas sp. in magnetically fixed-bed bioreactors and evaluation of the enzyme stability of immobilized bacteria.

Magnetically-modified Sphingomonas sp. was prepared using covalent binding of magnetic nanoparticles on to the cell surface. The magnetic modified bacteria were immobilized in the fixed-bed bioreactors (FBR) by internal and external magnetic fields for the biodetoxification of a model organophosphate, parathion: 93 % of substrate (50 mg parathion/l) was hydrolyzed at 0.5 ml/min in internal magnetic field fixed-bed bioreactor. The deactivation rate constants (at 1 ml/min) were 0.97 × 10(-3), 1.24 × 10(-3) and 4.17 × 10(-3) h(-1) for immobilized bacteria in external and internal magnetic field fixed-bed bioreactor and FBR, respectively. The deactivation rate constant for immobilized magnetically modified bacteria in external magnetic field fixed-bed bioreactor (EMFFBR) was 77 % lower than that of immobilized cells by entrapping method on porous basalt beads in FBR at 1 ml/min. Immobilized magnetic modified bacteria exhibited maximum enzyme stability in EMFFBR.

Immobilization of magnetic modified Flavobacterium ATCC 27551 using magnetic field and evaluation of the enzyme stability of immobilized bacteria.

The magnetic modified Flavobacterium sp. was prepared by covalently binding carboxylate-modified magnetic nanoparticles, and also, ionic adsorption of magnetic Fe(3)O(4) nanoparticles on the cell surface. The magnetic modified bacteria were immobilized by both internal and external magnetic fields. The pH stability and inherent resistance of the enzyme activity of the immobilized bacteria under acidic and alkaline conditions were increased. Immobilization of the magnetic modified bacteria using an external magnetic field improved the enzyme thermal stability. The results revealed that immobilization of the magnetic modified bacteria by an external magnetic field keeps 50% of the enzyme activity after 23.4, 16.6 and 6 h of incubation at 55 °C for the covalently binding of magnetic nanoparticles, the ionic adsorption of magnetic nanoparticles and the free cells, respectively. The results demonstrated the negative effect of various magnetic beads on the enzyme thermal stability of immobilized magnetic modified bacteria using an internal magnetic field.

Development of a model to predict partition coefficient of organic pollutants in cloud point extraction process.

A quantitative structure property relationship (QSPR) study has been performed to establish a model to relate structural descriptors of 45 organic compounds to their partition coefficients in water-hexadecylpyridinium chloride (CPC) micelles at 298K using partial least squares (PLS). 510 of six different categories of structural descriptors were calculated by Dragon software. The descriptors with 0.9 mutually pair correlations and with less than 0.1 with dependent variables were excluded at the early stage of the preprocessing of the structural data matrix. The data set was randomly divided into two groups: training set (40 molecules) and test set (5 molecules). In the final model 50 of the most effective of the structural descriptors on the partition coefficient were remained to model building by PLS calibration method. The optimum number of latent variables 5, which spanned 80% of the original variations of data matrix, was selected using leave one out cross validation method. Prediction ability of the model was tested by prediction of the partition coefficients of five unknown compounds and the mean relative error of prediction was 3.6%. The outliers were treated using leverage and score plots of the first third principal components. The efficiency of the new model was compared with Abraham model and it was found that the proposed model has more prediction ability.