Isolation of glycolonitrile-hydrolyzing microorganism based on colorimetric reaction

Nitrilase: a promising biocatalyst in industrial applications for green chemistry

Nitrilases are widely distributed in nature and are able to hydrolyze nitriles into their corresponding carboxylic acids and ammonia. In industry, nitrilases have been used as green biocatalysts for the production of high value-added products. To date, biocatalysts are considered to be important alternatives to chemical catalysts due to increasing environmental problems and resource scarcity. This review provides an overview of recent advances of nitrilases in aspects of distribution, enzyme screening, molecular structure and catalytic mechanism, protein engineering, and their potential applications in industry.

Enhanced bioconversion of ethylene glycol to glycolic acid by a newly isolated Burkholderia sp. EG13

Burkholderia sp. EG13 with high ethylene glycol-oxidizing activity was isolated from soil, which could be used for the synthesis of glycolic acid from the oxidation of ethylene glycol. Using the resting cells of Burkholderia sp. EG13 as biocatalysts, the optimum reaction temperature and pH were 30 °C and 6.0, respectively. After 24 h of biotransformation, the yield of glycolic acid from 200 mM ethylene glycol was 98.8 %. Furthermore, an integrated bioprocess for the production of glycolic acid which involved in situ product removal (ISPR) was investigated. Using fed-batch method with ISPR, a total of 793 mM glycolic acid has been accumulated in the reaction mixture after the 4th feed.

Effect of physicochemical parameters on nitrile-hydrolyzing potentials of newly isolated nitrilase of Fusarium oxysporum f. sp. lycopercisi ED-3

In recent years, nitrilases from fungus have received increasing attention, and most of the studies are performed on nitrilases of bacterial origin. Frequently used methods are based on analytical methods such as high-performance liquid chromatography, liquid chromatography-mass spectrometry, and gas chromatography; therefore, an efficient, user friendly, and rapid method has been developed to screen nitrilase enzyme based on the principle of color change of a pH indicator. Phenol red amended with the minimal medium appears light yellow at neutral pH, which changes into pink with the formation of ammonia, indicating nitrilase activity in the reaction medium. A highly potent strain ED-3 identified as Fusarium oxysporum f. sp. lycopercisi (specific activity 17.5 µmol/Min/mg dcw) was isolated using this method. The nitrilase activity of F. oxysporum f. sp. lycopercisi ED-3 strain showed wide substrate specificity toward aliphatic nitriles, aromatic nitriles, and orthosubstituted heterocyclic nitriles. 4-Aminobenzonitrile was found to be a superior substrate among all the nitriles used in this study. This nitrilase was active within pH 5-10 and temperature ranging from 25 to 60 °C with optimal at pH 7.0 and temperature at 50 °C. The nitrilase activity was enhanced to several folds through optimization of culture and biotransformation conditions from 1,121 to 1,941 µmol/Min.

Microbial transformation of nitriles to high-value acids or amides

Biotransformation of nitriles mediated by nitrile-amide converting enzymes has attracted considerable attention and developed tremendously in the recent years in China since it offers a valuable alternative to traditional chemical reaction which requires harsh conditions. As a result, an upsurge of these promising enzymes (including nitrile hydratase, nitrilase and amidase) has been taking place. This review aims at describing these enzymes in detail. A variety of microorganisms harboring nitrile-amide converting activities have been isolated and identified in China, some of which have already applied with moderate success. Currently, a wide range of high-value compounds such as aliphatic, alicyclic, aromatic and heterocyclic amides and their corresponding acids were provided by these nitrile-amide degrading organisms. Simultaneously, with the increasing demand of chiral substances, the enantioselectivity of the nitrilase superfamily is widely investigated and exploited in China, especially the bioconversion of optically active alpha-substituted phenylacetamides, acids and 2,2-dimethylcyclopropanecarboxamide and 2,2-dimethylcyclopropanecarboxylic acid by means of the catalysts exhibiting excellent stereoselectivity. Besides their synthetic value, the nitrile-amide converting enzymes also play an important role in environmental protection. In this context, cloning of the genes and expression of these enzymes are presented. In the near future in China, an increasing number of novel nitrile-amide converting organisms will be screened and their potential in the synthesis of useful acids and amides will be further exploited.

Nitrilases in nitrile biocatalysis: recent progress and forthcoming research

Over the past decades, nitrilases have drawn considerable attention because of their application in nitrile degradation as prominent biocatalysts. Nitrilases are derived from bacteria, filamentous fungi, yeasts, and plants. In-depth investigations on their natural sources function mechanisms, enzyme structure, screening pathways, and biocatalytic properties have been conducted. Moreover, the immobilization, purification, gene cloning and modifications of nitrilase have been dwelt upon. Some nitrilases are used commercially as biofactories for carboxylic acids production, waste treatment, and surface modification. This critical review summarizes the current status of nitrilase research, and discusses a number of challenges and significant attempts in its further development. Nitrilase is a significant and promising biocatalyst for catalytic applications.

Enzymatic production of 2-amino-2,3-dimethylbutyramide by cyanide-resistant nitrile hydratase

A novel enzymatic route for the synthesis of 2-amino-2,3-dimethylbutyramide (ADBA), important intermediate of highly potent and broad-spectrum imidazolinone herbicides, from 2-amino-2,3-dimethylbutyronitrile (ADBN) was developed. Strain Rhodococcus boritolerans CCTCC M 208108 harboring nitrile hydratase (NHase) towards ADBN was screened through a sophisticated colorimetric screening method and was found to be resistant to cyanide (5 mM). Resting cells of R. boritolerans CCTCC M 208108 also proved to be tolerant against high product concentration (40 g l−1) and alkaline pH (pH 9.3). A preparative scale process for continuous production of ADBA in both aqueous and biphasic systems was developed and some key parameters of the biocatalytic process were optimized. Inhibition of NHase by cyanide dissociated from ADBN was successfully overcome by temperature control (at 10°C). The product concentration, yield and catalyst productivity were further improved to 50 g l−1, 91% and 6.3 g product/g catalyst using a 30/70 (v/v) n-hexane/water biphasic system. Furthermore, cells of R. boritolerans CCTCC M 208108 could be reused for at lease twice by stopping the continuous reaction before cyanide concentration rose to 2 mM, with the catalyst productivity increasing to 12.3 g product/g catalyst. These results demonstrated that enzymatic synthesis of ADBA using whole cells of R. boritolerans CCTCC M 208108 showed potential for industrial application.

Screening, cultivation, and biocatalytic performance of Rhodococcus boritolerans FW815 with strong 2,2-dimethylcyclopropanecarbonitrile hydratase activity

In this work, a mild, efficient bioconversion of 2,2-dimethylcyclopropanecarbonitrile (DMCPCN) to 2,2-dimethylcyclopropanecarboxamide (DMCPCA) in distilled water system was developed. The isolate FW815 was screened using the enrichment culture technique, displaying strong DMCPCN hydratase activity, and was identified as Rhodococcus boritolerans based on morphological, physiological, biochemical tests and 16S rRNA gene sequencing. Cultivation outcomes indicated that R. boritolerans FW815 was a neutrophile, with a growth optimum of 28-32°C; its DMCPCN hydratase belonged to the Fe-type family, and was most active at 38-42°C, pH 7.0, with maximal activity of 4.51 × 10(4) U g(-1) DCW. R. boritolerans FW815 was found to be DMCPCA amidase-negative, eliminating the contamination of dimethylcyclopropanecarboxylic acid. Moreover, it displayed high activity and acceptable reusability in the non-buffered distilled water system, comparable to those in pH 7.0 phosphate buffer (50.0 mmol l(-1)).