A novel synthesis of iminodiacetic acid: Biocatalysis by whole Alcaligenes faecalis ZJB-09133 cells from iminodiacetonitrile

Preparation of regenerable magnetic nanoparticles for cellulase immobilization: Improvement of enzymatic activity and stability

To obtain regenerable magnetic nanoparticles, triethoxy(3-isocyanatopropyl)silane and iminodiacetic acid (IZ) were used as the starting material and immobilized on Fe₃ O₄ nanoparticles. Copper ions (Cu²⁺ ions) were loaded on the Fe-IZ nanoparticles and used for cellulase immobilization. The support was characterized by spectroscopic methods (FTIR, NMR) and thermogravimetric analysis, transmission electron microscopy, scanning electron microscope, X-ray diffraction, energy dispersive X-ray analysis, and vibrating sample magnetometer techniques. As a result of experiments, the amount of protein bound to immobilized cellulase (Fe-IZ-Cu-E) and cellulase activity was found to be 33.1 mg/g and 154 U/g at pH 5, 50°C, for 3 h. The results indicated that the free cellulase had kept only 50% of its activity after 2 h, while the Fe-IZ-Cu-E was observed to be around 77%, at 60°C. It was found that the immobilized cellulase maintained 93% of its initial catalytic activity after its sixth use. Furthermore, the Fe-IZ-Cu-E retained about 75% of its initial activity after 28 days of storage. To reuse the support material (Fe-IZ-Cu), it was regenerated by thorough washing with ammonia or imidazole.

Significant improvement of the nitrilase activity by semi-rational protein engineering and its application in the production of iminodiacetic acid

Iminodiacetic acid (IDA) is widely used as an intermediate in the manufacturing of chelating agents, glyphosate herbicides and surfactants. To improve activity and tolerance to the substrate for IDA production, Acidovorax facilis nitrilase was selected for further modification by the gene site saturation mutagenesis method. After screened by a two-step screening method, the best mutant (Mut-F168V/T201N/S192F/M191T/F192S) was selected. Compared to the wild-type nitrilase, Mut-F168V/T201N/S192F/M191T/F192S showed 136% improvement in specific activity. Co²⁺ stimulated nitrilase activity, whereas Cu²⁺, Zn²⁺ and Tween 80 showed a strong inhibitory effect. The V_max and k_cat of Mut-F168V/T201N/S192F/M191T/F192S were enhanced 1.23 and 1.23-fold, while the K_m was decreased 1.53-fold. The yield of Mut-F168V/T201N/S192F/M191T/F192S with 453.2 mM of IDA reached 71.9% in 5 h when 630 mM iminodiacetonitrile was used as substrate. This study indicated that mutant nitrilase obtained in this study is promising in applications for the upscale production of IDAN.

Bioconversion of Iminodiacetonitrile to Iminodiacetic acid with whole cells of Lysinibacillus boronitolerans MTCC 107614 (IICT-akl252)

Biotechnological potential of nitrilases are prompting significant interest in finding the novel microbes capable of hydrolyzing nitriles. In this view, we have screened about 450 bacterial strains for nitrilase production using bioconversion of iminodiacetonitrile (IDAN) to iminodiacetic acid (IDA) through hydrolysis and obtained six nitrilase-producing isolates. Among these six isolates, IICT-akl252 was promising which was identified as Lysinibacillus boronitolerans. This is the first report on L. boronitolerans for nitrilase activity. Optimization of various medium and reaction parameters for maximizing the nitrilase production using whole cells in shake flask was carried out for L. boronitolerans IICT-akl252. Sucrose (2 %) as a carbon source attained better nitrilase yield while IDAN appeared to be the preferable inducer (0.2 %). The maximum IDA formation was achieved with 100 mM IDAN and 150 mg/ml cells at 30 °C and pH 6.5. After optimization of the culture and reaction conditions, the activity of nitrilase was increased by 2.3-fold from 27.2 to 64.5 U. The enzyme was stable up to 1 h at 50 °C. The enzyme was able to hydrolyze aliphatic, aromatic and heterocyclic nitrile substrates.

Characterization of a nitrilase from Arthrobacter aurescens CYC705 for synthesis of iminodiacetic acid

A nitrilase gene cyc705 from Arthrobacter aurescens CYC705 for synthesis of iminodiacetic acid (IDA) was cloned. This gene contained a 930 bp ORF, which encoded a polypeptide of 310 amino acids. A recombinant Escherichia coli BL21(DE3)/pET28a-cyc705 was constructed to achieve the heterologous expression of cyc705. This recombinant nitrilase was purified to homogeneity with a molecular weight of 36.7 kDa on SDS-PAGE and mass spectrometry, and characterized to be an oligomer of 14 subunits by gel permeation chromatography. Using iminodiacetonitrile (IDAN) as the substrate, the Vmax, Km, kcat and kcat/Km were 9.05 U mg(-1), 43.17 mM(-1), 94.1 min(-1) and 2.18×10(3) min(-1) M(-1), respectively. The optimum temperature and pH were 25°C and 5.8. The suitable substrates for the purified nitrilase were short-chain aliphatic dinitriles. High concentration of IDAN could be hydrolyzed to IDA in a shorter time.

Screening and Improving the Recombinant Nitrilases and Application in Biotransformation of Iminodiacetonitrile to Iminodiacetic Acid

In this study, several nitrilase genes from phylogenetically distinct organisms were expressed and purified in E. coli in order to study their ability to mediate the biotransformation of nitriles. We identified three nitrilases: Acidovorax facilis nitrilase (AcN); Alcaligenes fecalis nitrilase (AkN); and Rhodococcus rhodochrous nitrilase (RkN), which catalyzed iminodiacetonitrile (IDAN) to iminodiacetic acid (IDA). AcN demonstrated 8.8-fold higher activity for IDAN degradation as compared to AkN and RkN. Based on homology modeling and previously described ‘hot spot’ mutations, several AcN mutants were screened for improved activity. One mutant M3 (F168V/L201N/S192F) was identified, which demonstrates a 41% enhancement in the conversion as well as a 2.4-fold higher catalytic efficiency towards IDAN as compared to wild-type AcN.

Efficient asymmetric reduction of 4-(trimethylsilyl)-3-butyn-2-one by Candida parapsilosis cells in an ionic liquid-containing system

Hydrophilic ionic liquids (ILs) were employed as green solvents to construct an IL-containing co-solvent system for improving the asymmetric reduction of 4-(trimethylsilyl)-3-butyn-2-one by immobilized Candida parapsilosis cells. Among 14 hydrophilic ILs examined, 1-(2'-hydroxyl)ethyl-3-methylimidazolium nitrate (C(2)OHMIM·NO(3)) was considered as the most suitable IL for the bioreduction with the fastest initial reaction rate, the highest yield and the highest product e.e., which may be due to the good biocompatibility with the cells. For a better understanding of the bioreduction performed in the C(2)OHMIM·NO(3)-containing co-solvent system, the effects of several crucial variables were systematically investigated. The optimal C(2)OHMIM·NO(3) content, substrate concentration, buffer pH, co-substrate concentration and temperature were 10% (v/v), 3.0 mmol/L, 5.0, 98.1 mmol/L and 30°C, respectively. Under the optimal conditions, the initial reaction rate, the maximum yield and the product e.e. were 17.3 µmol/h g(cell), 95.2% and >99.9%, respectively, which are much better than the corresponding results previously reported. Moreover, the immobilized cells remained more than 83% of their initial activity even after being used repeatedly for 10 batches in the C(2)OHMIM·NO(3)-containing system, exhibiting excellent operational stability.

Gene cloning, expression, and characterization of a nitrilase from Alcaligenes faecalis ZJUTB10

Nitrilases are important industrial enzymes that convert nitriles directly into the corresponding carboxylic acids. In the current work, the fragment with a length of 1068 bp that encodes the A. faecalis ZJUTB10 nitrilase was obtained. Moreover, a catalytic triad was proposed and verified by site-directed mutagenesis, and the detailed mechanism of this nitrilase was clarified. The substrate specificity study demonstrated that the A. faecalis ZJUTB10 nitrilase belongs to the family of arylacetonitrilases. The optimum pH and temperature for the purified nitrilase was 7-8 and 40 °C, respectively. Mg(2+) stimulated hydrolytic activity, whereas Cu(2+), Co(2+), Ni(2+), Ag(+), and Hg(2+) showed a strong inhibitory effect. The K(m) and v(max) for mandelonitrile were 4.74 mM and 15.85 μmol min(-1) mg(-1) protein, respectively. After 30 min reaction using the nitrilase, mandelonitrile at the concentration of 20 mM was completely hydrolyzed and the enantiomeric excess against (R)-(-)-mandelic acid was >99%. Characteristics investigation indicates that this nitrilase is promising in catalysis applications.