On the Mechanism of Nitriles Toxicity

A simple, efficient and rapid screening technique for differentiating nitrile hydratase and nitrilase producing bacteria

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A rapid dye based plate screening method for nitrile hydrolyzing enzymes.

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Method identifies the end products of nitrile hydrolyzing enzymes.

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The method differentiates between nitrile hydratase and nitrilase producing bacteria.

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A potential NHase producing bacterial strain was identified as Rhodococcus rhodochrous.

Nitrile hydrolyzing enzymes catalyze the hydration of nitrile compounds to corresponding amides and acids. Bacteria, isolated from soil samples were screened for nitrile hydrolyzing enzymes by simple dye based 96 well plate and nesslerization method. Bromothymol blue was used as an indicator for the detection of amides and acids based on colour change of the indicator dye from blue to dark green or yellow. The screening assay also differentiates between nitrile hydratase (NHase) and nitrilase producing bacteria. Among the 108 bacterial strains screened for enzyme activity, six strains were positive for NHase activity and eleven strains were positive for nitrilase activity based on their ability to degrade acrylonitrile into products. The strain showing maximum NHase activity in quantitative assay was identified as Rhodococcus rhodochrous. The modified method developed by us would be useful for rapid screening of nitrile degrading bacteria potent for acrylamide/acrylic acid production when acrylonitrile is supplied as substrate.

Time-Course Evaluation of Iminodipropionitrile-Induced Liver and Kidney Toxicities in Rats: A Biochemical, Molecular and Histopathological Study

Iminodipropionitrile (IDPN) is known to produce axonopathy and vestibular hair cell degeneration. Recent histopathological studies have shown IDPN-induced liver and kidney toxicities in rodents; however, the associated mechanisms are not clearly understood. We investigated the role of proinflammatory cytokines in IDPN-induced liver and kidney toxicities in rats. Rats were treated with saline (control) and IDPN (100 mg/kg, intraperitoneally) daily for 1, 5, and 10 days, respectively. Animals were killed 24 hours after the last dose and liver and kidneys were collected for histopathology and interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α messenger RNA expression analysis. Serum aspartate aminotransferase and alanine aminotransferase activities were significantly increased after 10 doses of IDPN. The level of serum creatinine was initially increased after the first dose of IDPN but subsided on days 5 and 10. Blood urea nitrogen levels were significantly increased on days 5 and 10 following IDPN exposure. Histopathology showed dose-dependent hepatotoxicity in IDPN-treated rats. Iminodipropionitrile-induced expression of proinflammatory cytokines peaked after day 1 in liver and after day 5 in kidneys. In conclusion, repeated exposure of IDPN for 10 days produced significant structural and functional damages in rat liver whereas kidneys showed gradual recovery with time. These findings point toward the role of inflammatory mediators in IDPN-induced toxicity in rats.

Hydrolytic denitrification and decynidation of acrylonitrile in wastewater with Arthrobacter nitroguajacolicus ZJUTB06-99

Acrylonitrile (C₃H₃N) widely used in chemical raw materials has biological toxicity with -CN bond, so it is the key to removal of cyanide from acrylonitrile wastewater. In our previous research and investigation, a strain was identified as Arthrobacter nitroguajacolicus named ZJUTB06-99 and was proved to be capable of degrading acrylonitrile. In this paper, the strain ZJUTB06-99 was domesticated with acrylonitrile-containing medium and its decyanidation and denitrification in simulated acrylonitrile wastewater were studied. The intermediate product of acrylonitrile in degradation process was identified through gas chromatography-mass spectrometer, as well as the biodegradation pathway of acrylonitrile in wastewater was deduced tentatively. The kinetics equation of biodegradation of acrylonitrile was lnC = - 0.1784t + 5.3349, with the degradation half-life of acrylonitrile in wastewater by 3.885 h. The results of this study showed that the optimum levels of temperature, pH and bacteria concentration to attain the maximum biodegradation were obtained as 30 °C, 6 and 100 g/L, respectively. The disadvantages of the biodegradation with this strain and its possible enhanced method to degrade acrylonitrile in wastewater were also discussed.

Combination of a recombinant bacterium with organonitrile-degrading and biofilm-forming capability and a positively charged carrier for organonitriles removal

The immobilization of organonitrile-degrading bacteria via the addition of biofilm-forming bacteria represents a promising technology for the treatment of organonitrile-containing wastewater, but biofilm-forming bacteria simply mixed with degrading bacteria may reduce the biodegradation efficiency. Nitrile hydratase and amidase genes, which play critical roles in organonitriles degradation, were cloned and transformed into the biofilm-forming bacterium Bacillus subtilis N4 to construct a recombinant bacterium B. subtilis N4/pHTnha-ami. Modified polyethylene carriers with positive charge was applied to promote bacterial adherence and biofilm formation. The immobilized B. subtilis N4/pHTnha-ami was resistant to organonitriles loading shocks and could remove organic cyanide ion with a initial concentration of 392.6 mg/L for 24 h in a moving bed biofilm reactor. The imputed quorum-sensing signal and the high-throughput sequencing analysis of the biofilm indicated that B. subtilis N4/pHTnha-ami was successfully immobilized and became dominant. The successful application of the immobilized recombinant bacterium offers a novel strategy for the biodegradation of recalcitrant compounds.

Enzymatic degradation of aliphatic nitriles by Rhodococcus rhodochrous BX2, a versatile nitrile-degrading bacterium

Nitriles are common environmental pollutants, and their removal has attracted increasing attention. Microbial degradation is considered to be the most acceptable method for removal. In this work, we investigated the biodegradation of three aliphatic nitriles (acetonitrile, acrylonitrile and crotononitrile) by Rhodococcus rhodochrous BX2 and the expression of their corresponding metabolic enzymes. This organism can utilize all three aliphatic nitriles as sole carbon and nitrogen sources, resulting in the complete degradation of these compounds. The degradation kinetics were described using a first-order model. The degradation efficiency was ranked according to t1/2 as follows: acetonitrile>trans-crotononitrile>acrylonitrile>cis-crotononitrile. Only ammonia accumulated following the three nitriles degradation, while amides and carboxylic acids were transient and disappeared by the end of the assay. mRNA expression and enzyme activity indicated that the tested aliphatic nitriles were degraded via both the inducible NHase/amidase and the constitutive nitrilase pathways, with the former most likely preferred.

Molecular products from the thermal degradation of glutamic acid

The thermal behavior of glutamic acid was investigated in N2 and 4% O2 in N2 under flow reactor conditions at a constant residence time of 0.2 s, within a total pyrolysis time of 3 min at 1 atm. The identification of the main pyrolysis products has been reported. Accordingly, the principal products for pyrolysis in order of decreasing abundance were succinimide, pyrrole, acetonitrile, and 2-pyrrolidone. For oxidative pyrolysis, the main products were succinimide, propiolactone, ethanol, and hydrogen cyanide. Whereas benzene, toluene, and a few low molecular weight hydrocarbons (propene, propane, 1-butene, and 2-butene) were detected during pyrolysis, no polycyclic aromatic hydrocarbons (PAHs) were detected. Oxidative pyrolysis yielded low molecular weight hydrocarbon products in trace amounts. The mechanistic channels describing the formation of the major product succinimide have been explored. The detection of succinimide (major product) and maleimide (minor product) from the thermal decomposition of glutamic acid has been reported for the first time in this study. Toxicological implications of some reaction products (HCN, acetonitrile, and acyrolnitrile), which are believed to form during heat treatment of food, tobacco burning, and drug processing, have been discussed in relation to the thermal degradation of glutamic acid.