Generation of mutant of Rhodococcus rhodochrous PA-34 through chemical mutagenesis for hyperproduction of nitrile hydratase

Biotransformation of 3-cyanopyridine to nicotinic acid using whole-cell nitrilase of Gordonia terrae mutant MN12

In the present study, the Gordonia terrae was subjected to chemical mutagenesis using ethyl methane sulfonate (EMS) and methyl methane sulfonate (MMS), N-methyl-N-nitro-N-nitrosoguanidine (MNNG), 5-bromouracil (5-BU) and hydroxylamine with the aim of improving the catalytic efficiency of its nitrilase for conversion of 3-cyanopyridine to nicotinic acid. A mutant MN12 generated with MNNG exhibited increase in nitrilase activity from 0.5 U/mg dcw (dry cell weight) (in the wild G. terrae) to 1.33 U/mg dcw. Further optimizations of culture conditions using response surface methodology enhanced the enzyme production to 1.2-fold. Whole-cell catalysis was adopted for bench-scale synthesis of nicotinic acid, and 100% conversion of 100 mM 3-cyanopyridine was achieved in potassium phosphate buffer (0.1 M, pH 8.0) at 40 °C in 15 min. The whole-cell nitrilase of the mutant MN12 exhibited higher rate of product formation and volumetric productivity, i.e., 24.56 g/h/g dcw and 221 g/L as compared to 8.95 g/h/g dcw and 196.8 g/L of the wild G. terrae. The recovered product was confirmed by HPLC, FTIR and NMR analysis with high purity (> 99.9%). These results indicated that the mutant MN12 of G. terrae as whole-cell nitrilase is a very promising biocatalyst for the large-scale synthesis of nicotinic acid.

Nanocarriers-based immobilization of enzymes for industrial application

Nanocarriers-based immobilization strategies are a novel concept in the enhancement of enzyme stability, shelf life and efficiency. A wide range of natural and artificial supports have been assessed for their efficacy in enzyme immobilization. Nanomaterials epitomize unique and fascinating matrices for enzyme immobilization. These structures include carbon nanotubes, superparamagnetic nanoparticles and nanofibers. These nano-based supports offer stable attachment of enzymes, thus ensuring their reusability in diverse industrial applications. This review attempts to encompass recent developments in the critical role played by nanotechnology towards the improvement of the practical applicability of microbial enzymes. Nanoparticles are increasingly being used in combination with various polymers to facilitate enzyme immobilization. These endeavors are proving to be conducive for enzyme-catalyzed industrial operations. In recent years the diversity of nanomaterials has grown tremendously, thus offering endless opportunities in the form of novel combinations for various biotransformation experimentations. These nanocarriers are advantageous for both free enzymes and whole-cell immobilization, thus demonstrating to be relatively effective in several fermentation procedures.

Nitrile hydratase mediated green synthesis of lactamide by immobilizing Rhodococcus pyridinivorans NIT-36 cells on N, N'-Methylene bis-acrylamide activated chitosan

In this paper green synthesis of an important commodity chemical lactamide has been undertaken using chitosan immobilized Rhodococcus pyridinivorans NIT-36 harbouring nitrile hydratase (NHase) enzyme. The cells immobilization (300 mg/g) is based on the partial entrapment of cells by suspension cross-linking technique facilitated by N, N'-Methylene bis-acrylamide. In the repeated-use experiments, the immobilized cells retained 80% of its initial activity when stored at 4 °C for 30 days. NHase activity of free and immobilized cells was studied over temperature ranging from 25 °C to 60 °C. The activity for free cells showed a sharp decline of 70% when the reaction temperature was elevated from 45 °C to 50 °C whereas chitosan immobilized cells retained their activity in the same temperature range. A fed-batch reaction was designed and the immobilized cells showed 100% similar enzymatic pattern for five consecutive rounds which gradually decreased in following cycles. A volumetric productivity of 20 g/L and catalytic productivity of 8.33 g/g dcw/h for lactamide were achieved.

Random Mutagenesis of Thermophilic Xylanase for Enhanced Stability and Efficiency Validated through Molecular Docking

BACKGROUND

Xylanases of thermophilic origin are more robust and stable and hence more suitable for industrial applications. The aim of the research was to develop a patent using a robust mutant exhibiting enhanced xylanase activity. The strain (Bacillus aestuarii SC-2014) subjected to mutagenesis is thermophilic in origin and hence it is envisioned that the enhancement of its catalytic potential will enhance its industrial applicability.

OBJECTIVE

The main aim was to develop a stable and vigorous mutant having higher xylanase activity and improved thermostability.

METHODS

The bacterial strain isolated from the Tattapani hot springs of Himachal Pradesh (India) was mutagenized by single separate exposure of Ethyl methane sulphonate (EMS) and N-methyl N-nitro N-nitrosoguanidine (MNNG).

RESULTS

A mutant library was generated and extensive screening led to the identification of the most potent mutant strain selected and designated as Bacillus sp. SC-2014 EMS200 (MTCC number 25046) which displayed not only enhanced xylanase activity and thermo stability but also appreciable genetic stability. This strain displayed a 3-fold increase in enzyme activity and simultaneously, a significant reduction in fermentation time from 72 h to 48 h was also observed. The xylanase gene from wild and mutant strain was cloned, sequenced and subjected to molecular docking. Two mutations H121D and S123T were present inside the binding pocket.

CONCLUSION

Mutation H121D made the binding pocket more acidic and charged, thus enhancing the xylanase activity for mutant protein. Mutations also resulted in charged amino acids (Y99K and H121D) which were identified as a probable cause for enhancing the thermostability of mutant protein.

Purification and characterization of nitrile hydratase of mutant 4D of Rhodococcus rhodochrous PA-34

Nitrile hydratase (NHase; E.C. 4.2.1.84) has been purified and characterized using ammonium sulfate precipitation, ion exchange chromatography and gel filtration chromatography from the mutant 4D of Rhodococcus rhodochrous PA-34. The SDS-PAGE and MALDI-TOF analysis of the purified enzyme revealed that it is dimmer consisting of α- and β-subunits with a molecular mass of 25 and 30 kDa, respectively. The K_m and V_max values were 102 mM and 350.8 μmol/min/mg using 3-cyanopyridine as substrate. The purified NHase was stable in higher concentration of potassium ions and in acidic pH 5.5 as compared to NHase of the wild R. rhodochrous PA-34. The analysis of the N-terminal amino acid sequence of this enzyme revealed that this enzyme has 90 % homology with the high molecular weight nitrile hydratase of R. rhodochrous J1.

Cloning, sequencing, and expression of nitrile hydratase gene of mutant 4D strain of Rhodococcus rhodochrous PA 34 in E. coli

The NHase encoding gene of mutant 4D was isolated by PCR amplification. The NHase gene of mutant 4D was successfully cloned and expressed in Escherichia coli by using Ek/LIC Duet cloning kits (Novagen). For the active expression of the NHase gene, the co-expression of small cobalt transporter gene (P-protein gene) has also been co-expressed with NHase gene E. coli. The nucleotide sequence of this NHase gene revealed high homology with the H-NHase of Rhodococcus rhodochrous J1. The recombinant E. coli cells showed higher NHase activity (5.9 U/mg dcw) as compared to the wild (4.1 U/mg dcw) whereas it is less than the mutant strain (8.4 U/mg dcw). Addition of cobalt ion in Luria-Bertani medium is needed up to a very small concentration (0.4 mM) for NHase activity. The recombinant E. coli exhibited maximum NHase activity at 6 h of incubation and was purified with a yield of 56 % with specific activity of 37.1 U/mg protein.