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Characterization of a nitrilase and a nitrile hydratase from Pseudomonas sp. strain UW4 that converts indole-3-acetonitrile to indole-3-acetic acid.

ABSTRACT: Indole-3-acetic acid (IAA) is a fundamental phytohormone with the ability to control many aspects of plant growth and development. Pseudomonas sp. strain UW4 is a rhizospheric plant growth-promoting bacterium that produces and secretes IAA. While several putative IAA biosynthetic genes have been reported in this bacterium, the pathways leading to the production of IAA in strain UW4 are unclear. Here, the presence of the indole-3-acetamide (IAM) and indole-3-acetaldoxime/indole-3-acetonitrile (IAOx/IAN) pathways of IAA biosynthesis is described, and the specific role of two of the enzymes (nitrilase and nitrile hydratase) that mediate these pathways is assessed. The genes encoding these two enzymes were expressed in Escherichia coli, and the enzymes were isolated and characterized. Substrate-feeding assays indicate that the nitrilase produces both IAM and IAA from the IAN substrate, while the nitrile hydratase only produces IAM. The two nitrile-hydrolyzing enzymes have very different temperature and pH optimums. Nitrilase prefers a temperature of 50°C and a pH of 6, while nitrile hydratase prefers 4°C and a pH of 7.5. Based on multiple sequence alignments and motif analyses, physicochemical properties and enzyme assays, it is concluded that the UW4 nitrilase has an aromatic substrate specificity. The nitrile hydratase is identified as an iron-type metalloenzyme that does not require the help of a P47K activator protein to be active. These data are interpreted in terms of a preliminary model for the biosynthesis of IAA in this bacterium.

SUBMITTER: Duca D

PROVIDER: S-EPMC4148799 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Characterization of a nitrilase and a nitrile hydratase from Pseudomonas sp. strain UW4 that converts indole-3-acetonitrile to indole-3-acetic acid.

Duca Daiana D Rose David R DR Glick Bernard R BR

Applied and environmental microbiology 20140801 15

Indole-3-acetic acid (IAA) is a fundamental phytohormone with the ability to control many aspects of plant growth and development. Pseudomonas sp. strain UW4 is a rhizospheric plant growth-promoting bacterium that produces and secretes IAA. While several putative IAA biosynthetic genes have been reported in this bacterium, the pathways leading to the production of IAA in strain UW4 are unclear. Here, the presence of the indole-3-acetamide (IAM) and indole-3-acetaldoxime/indole-3-acetonitrile (IA ...[more]

PMID: 24837382

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Project description:Variovorax is a metabolically diverse genus of plant growth-promoting rhizobacteria (PGPR) that engages in mutually beneficial interactions between plants and microbes. Unlike most PGPR, Variovorax cannot synthesize the phytohormone indole-3-acetic acid (IAA) via tryptophan. However, we found that Variovorax boronicumulans strain CGMCC 4969 can produce IAA using indole-3-acetonitrile (IAN) as the precursor. Thus, in the present study, the IAA synthesis mechanism of V. boronicumulans CGMCC 4969 was investigated. V. boronicumulans CGMCC 4969 metabolized IAN to IAA through both a nitrilase-dependent pathway and a nitrile hydratase (NHase) and amidase-dependent pathway. Cobalt enhanced the metabolic flux via the NHase/amidase, by which IAN was rapidly converted to indole-3-acetamide (IAM) and in turn to IAA. IAN stimulated metabolic flux via the nitrilase, by which IAN was rapidly converted to IAA. Subsequently, the IAA was degraded. V. boronicumulans CGMCC 4969 can use IAN as the sole carbon and nitrogen source for growth. Genome sequencing confirmed the IAA synthesis pathways. Gene cloning and overexpression in Escherichia coli indicated that NitA has nitrilase activity and IamA has amidase activity to respectively transform IAN and IAM to IAA. Interestingly, NitA showed a close genetic relationship with the nitrilase of the phytopathogen Pseudomonas syringae Quantitative PCR analysis indicated that the NHase/amidase system is constitutively expressed, whereas the nitrilase is inducible. The present study helps our understanding of the versatile functions of Variovorax nitrile-converting enzymes that mediate IAA synthesis and the interactions between plants and these bacteria.IMPORTANCE We demonstrated that Variovorax boronicumulans CGMCC 4969 has two enzymatic systems-nitrilase and nitrile hydratase/amidase-that convert indole-3-acetonitrile (IAN) to the important plant hormone indole-3-acetic acid (IAA). The two IAA synthesis systems have very different regulatory mechanisms, affecting the IAA synthesis rate and duration. The nitrilase was induced by IAN, which was rapidly converted to IAA; subsequently, IAA was rapidly consumed for cell growth. The nitrile hydratase (NHase) and amidase system was constitutively expressed and slowly but continuously synthesized IAA. In addition to synthesizing IAA from IAN, CGMCC 4969 has a rapid IAA degradation system, which would be helpful for a host plant to eliminate redundant IAA. This study indicates that the plant growth-promoting rhizobacterium V. boronicumulans CGMCC 4969 has the potential to be used by host plants to regulate the IAA level.

Project description:BackgroundThe conversion of nitriles into amides or carboxylic acids by nitrilase has taken its application into consideration, as the scope of its applications has recently been extended.ObjectivesIn this study, P. aeruginosa RZ44 was isolated from sewage in the Kerman which has Nitrile-degradation activity. In order to improve the nitrilase production, several optimization were done on environmental condition. Nitrilase activity was characterized against different pHs, temperatures, ions, and substrates.Materials and methodsEnzyme activity was evaluated by determining the production of ammonia following to the modification of the phenol/hypochlorite method. Different factors that affect production of the enzyme by P. aeruginosa RZ44 were optimized and evaluated in the culture mediums.ResultsThe results showed that degradation of the acetonitrile by P. aeruginosa RZ44 increased the pH of the growth medium from the initial pH 7.0 to 9.37. Optimizing the medium for P. aeruginosa RZ44, it was found that glucose and starch (5 g.L-1) have strongly supported nitrilase production, compared to the control. As well, urea (5 g.L-1) and yeast extract (15 g.L-1) have favored an increased biomass and nitrilase production, as the nitrogen sources. These results show that nitrilase production increases in the pH range 5.0 to 7.0 and then start decreasing. Addition of the Mg2+, Fe2+ and Na+ has supported the biomass and nitrilase production. Co2+, Mn2+ and Cu2+ were confirmed to inhibit cell growth and enzyme production. Enzyme characterization results show that, P. aeruginosa RZ44 nitrilase exhibits comparatively high activity and stability at pH 7.0 and 40°C. Nitrilase was completely inhibited by CoCl2 and CaCl2, whereas, the inhibition in the presence of MnSO4 and CuSO4 was about 60%. Time course analysis of the nitrile conversion by the resting P. aeruginosa RZ44 cells showed that nitrile substrates (i.e. acetonitrile) was hydrolyzed within 8 h.Conclusionsthese results indicate that P. aeruginosa RZ44 has the potential to be applied in the biotransformation of nitrile compounds.

Dataset Information

Characterization of a nitrilase and a nitrile hydratase from Pseudomonas sp. strain UW4 that converts indole-3-acetonitrile to indole-3-acetic acid.

Publications

Characterization of a nitrilase and a nitrile hydratase from Pseudomonas sp. strain UW4 that converts indole-3-acetonitrile to indole-3-acetic acid.

Similar Datasets

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