Enzymatic degradation of nitriles by a Candida guilliermondii UFMG-Y65

Response surface methodology: An effective optimization strategy for enhanced production of nitrile hydratase (NHase) by Rhodococcus rhodochrous (RS-6)

Nitrile hydratase is an enzyme which catalyze the hydration of nitriles into amide and their role as catalysts for acrylamide production in industries are well known. The present study aims at statistically optimizing physiological and nutritional parameters for NHase production from Rhodococcus rhodochrous (RS-6). The effect of incubation period, temperature, pH, carbon and nitrogen sources on the production of NHase was investigated by one factor at a time strategy. Further optimization process was carried out by response surface methodology for studying the interactive effect of these variables using central composite design. The optimized levels of variables obtained by statistical analysis were: incubation period 48 h, temperature 33 °C, pH 7.0, glycerol 1% and urea 0.75%, which resulted in maximum NHase production. The results of ANOVA were significant with the F-value of the model being 296.78, value of R² is 0.9983 and the lack of fit test was not significant. The contour and response surface plots showed significant interaction between the variables. The NHase yield was enhanced up to 6.22 fold by statistical optimization using RSM. Thus, the developed experimental design is effective towards process optimization for NHase production from R. rhodochrous (RS-6).

Marine Microorganisms for Biocatalysis: Selective Hydrolysis of Nitriles with a Salt-Resistant Strain of Meyerozyma guilliermondii

A screening among marine yeasts was carried out for nitrile hydrolyzing activity. Meyerozyma guilliermondii LM2 (UBOCC-A-214008) was able to efficiently grow on benzonitrile and cyclohexanecarbonitrile (CECN) as sole nitrogen sources. A two-step one-pot method for obtaining cells of M. guilliermondii LM2 (UBOCC-A-214008) endowed with high nitrilase activity was established; the resulting whole cells converted different nitriles with high molar conversions and showed interesting enantioselectivity toward racemic substrates. Nitrilase from M. guilliermondii LM2 (UBOCC-A-214008) displayed high activity on aromatic substrates, but also arylaliphatic and aliphatic substrates were accepted. Salt-resistant M. guilliermondii LM2 (UBOCC-A-214008) was used in media with different salinity, being highly active up to 1.5 M NaCl concentration. Finally, hydrolysis of nitriles was efficiently performed using a bioprocess (yeast growth and biotransformation with resting cells) entirely carried out in seawater.

A review of the interactions between acrylamide, microorganisms and food components

Acrylamide (AA) and its metabolites have been recognized as potential carcinogens, but also they can cause other negative symptoms in human or animal organisms and therefore this class of chemical compounds has attracted a lot of attention.

Nitrile-converting enzymes: an eco-friendly tool for industrial biocatalysis

Nitriles are organic compounds bearing a − C ≡ N group; they are frequently known to occur naturally in both fauna and flora and are also synthesized chemically. They have wide applicability in the fields of medicine, industry, and environmental monitoring. However, the majority of nitrile compounds are considered to be lethal, mutagenic, and carcinogenic in nature and are known to cause potential health problems such as nausea, bronchial irritation, respiratory distress, convulsions, coma, and skeletal deformities in humans. Nitrile-converting enzymes, which are extracted from microorganisms, are commonly termed nitrilases and have drawn the attention of researchers all over the world to combat the toxicity of nitrile compounds. The present review focuses on the utility of nitrile-converting enzymes, sources, classification, structure, properties, and applications, as well as the future perspective on nitrilases.

Candida guilliermondii: biotechnological applications, perspectives for biological control, emerging clinical importance and recent advances in genetics

Candida guilliermondii (teleomorph Meyerozyma guilliermondii) is an ascomycetous species belonging to the Saccharomycotina CTG clade which has been studied over the last 40 years due to its biotechnological interest, biological control potential and clinical importance. Such a wide range of applications in various areas of fundamental and applied scientific research has progressively made C. guilliermondii an attractive model for exploring the potential of yeast metabolic engineering as well as for elucidating new molecular events supporting pathogenicity and antifungal resistance. All these research fields now take advantage of the establishment of a useful molecular toolbox specifically dedicated to C. guilliermondii genetics including the construction of recipient strains, the development of selectable markers and reporter genes and optimization of transformation protocols. This area of study is further supported by the availability of the complete genome sequence of the reference strain ATCC 6260 and the creation of numerous databases dedicated to gene ontology annotation (metabolic pathways, virulence, and morphogenesis). These genetic tools and genomic resources represent essential prerequisites for further successful development of C. guilliermondii research in medical mycology and in biological control by facilitating the identification of the multiple factors that contribute to its pathogenic potential. These genetic and genomic advances should also expedite future practical uses of C. guilliermondii strains of biotechnological interest by opening a window into a better understanding of the biosynthetic pathways of valuable metabolites.

Characterisation of the substrate specificity of the nitrile hydrolyzing system of the acidotolerant black yeast Exophiala oligosperma R1

The `black yeast' Exophiala oligosperma R1 can utilise various organic nitriles under acidic conditions as nitrogen sources. The induction of a phenylacetonitrile converting activity was optimised by growing the strain in the presence of different nitriles and /or complex or inorganic nitrogen sources. The highest nitrile hydrolysing activity was observed with cells grown with 2-cyanopyridine and NaNO₃. The cells metabolised the inducer and grew with 2-cyanopyridine as sole source of nitrogen. Cell extracts converted various (substituted) benzonitriles and phenylacetonitriles. They usually converted the isomers carrying a substituent in the meta-position with higher relative activities than the corresponding para- or ortho-substituted isomers. Aliphatic substrates such as acrylonitrile and 2-hydroxy-3-butenenitrile were also hydrolysed. The highest specific activity was detected with 4-cyanopyridine. Most nitriles were almost exclusively converted to the corresponding acids and no or only low amounts of the corresponding amides were formed. The cells hydrolysed amides only with extremely low activities. It was therefore concluded that the cells harboured a nitrilase activity. The specific activities of whole cells and cell extracts were compared for different nitriles and evidence obtained for limitation in the substrate-uptake by whole cells. The conversion of 2-hydroxy-3-butenenitrile to 2-hydroxy-3-butenoic acid at pH 4 demonstrated the unique ability of cells of E. oligosperma R1 to hydrolyse aliphatic α-hydroxynitriles under acidic conditions. The organism could grow with phenylacetonitrile as sole source of carbon, energy and nitrogen. The degradation of phenylacetonitrile presumably proceeds via phenylacetic acid, 2-hydroxyphenylacetic acid, 2,5-dihydroxyphenylacetic acid (homogentisate), maleylacetoacetate and fumarylacetoacetate.

Biodegradation of propionitrile by Klebsiella oxytoca immobilized in alginate and cellulose triacetate gel

A microbial process for the degradation of propionitrile by Klebsiella oxytoca was studied. The microorganism, K. oxytoca, was isolated from the discharged wastewater of metal plating factory in southern Taiwan and adapted for propionitrile biodegradation. The free and immobilized cells of K. oxytoca were then examined for their capabilities on degrading propionitrile under various conditions. Alginate (AL) and cellulose triacetate (CT) techniques were applied for the preparation of immobilized cells. The efficiency and produced metabolic intermediates and end-products of propionitrile degradation were monitored in bath and continuous bioreactor experiments. Results reveal that up to 100 and 150 mM of propionitrile could be removed completely by the free and immobilized cell systems, respectively. Furthermore, both immobilized cell systems show higher removal efficiencies in wider ranges of temperature (20-40 degrees C) and pH (6-8) compared with the free cell system. Results also indicate that immobilized cell system could support a higher cell density to enhance the removal efficiency of propionitrile. Immobilized cells were reused in five consecutive degradation experiments, and up to 99% of propionitrile degradation was observed in each batch test. This suggests that the activity of immobilized cells can be maintained and reused throughout different propionitrile degradation processes. A two-step pathway was observed for the biodegradation of propionitrile. Propionamide was first produced followed by propionic acid and ammonia. Results suggest that nitrile hydratase and amidase were involved in the degradation pathways of K. oxytoca. In the continuous bioreactor, both immobilized cells were capable of removing 150 mM of propionitriles completely within 16h, and the maximum propionitriles removal rates using AL and CT immobilized beads were 5.04 and 4.98 mM h(-1), respectively. Comparing the removal rates obtained from batch experiments with immobilized cells (AL and CT were 1.57 and 2.18 mM h(-1) at 150 mM of propionitrile, respectively), the continuous-flow bioreactor show higher potential for practical application.

Isolation and characterization of a nitrile hydrolysing acidotolerant black yeast-Exophiala oligosperma R1

Different nitriles were used as sole sources of nitrogen in a series of enrichments under acidic conditions to isolate acidotolerant nitriles hydrolysing microorganisms. From an enrichment in Na-citrate-phosphate buffer at pH 4 with glucose as carbon source and phenylacetonitrile as sole source of nitrogen, a black yeast (strain R1) was obtained which was identified by subsequent 18S rRNA gene sequencing as Exophiala oligosperma. The growth conditions of the organism were optimized for the production of cell material and the induction of the nitrile converting activity. Resting cell experiments demonstrated that phenylacetonitrile was converted via phenylacetic acid and 2-hydroxyphenylacetic acid. The organism could grow at pH 4 with phenylacetonitrile as sole source of carbon, nitrogen, and energy. The nitriles hydrolysing activity was also detected in cell-free extracts and indications for a nitrilase activity were found. The cell-free extracts converted, in addition to phenylacetonitrile, also different substituted phenylacetonitriles. Whole cells of E. oligosperma R1 converted phenylacetonitrile with almost the same reaction rates in the pH range from pH 1.5-pH 9.

Enzymatic degradation of nitriles by Klebsiella oxytoca

Klebsiella oxytoca, isolated from cyanide-containing wastewater, was able to utilize many nitriles as sole source of nitrogen. The major objective of this study was to explore the ability of K. oxytoca to utilize some nitriles and then further evaluate the pathways of transformation of cyanide compounds by K. oxytoca. Results from this study indicate that succinonitrile and valeronitrile were the most optimal sources of nitrogen for the growth of K. oxytoca. The biodegradation of acetonitrile proceeded with the formation of acetamide followed by acetic acid. The production of ammonia was also detected in this biodegradation experiment. Similar results were observed in the propionitrile biodegradation experiments. Collectively, this study suggests that the breakdown of acetonitrile or propionitrile by this bacterium was via a two-step enzymatic hydrolysis with amides as the intermediates and organic acids plus with ammonia as the end products.

Selective biotransformation of substituted alicyclic nitriles by Rhodococcus equi A4

Nitrile hydratase from Rhodococcus equi A4 discriminated between geometric isomers of substituted alicyclic nitriles. The enzyme transformed trans-4-benzoyloxycyclohexanecarbonitrile (trans-1a), cis-3-benzoyloxy cyclohexanecarbonitrile (cis-2a), trans-2-hydroxycyclohexanecarbonitrile (trans-3a), and trans-2-hydroxycyclo pentanecarbonitrile (trans-4a) into the corresponding amides. On the contrary, cis-2-hydroxycyclohexanecarbonitrile (cis-3a) and cis-2-hydroxycyclopentanecarbonitrile (cis-4a) were not converted to a significant extent. cis-4-Ben zoyl oxycyclohexanecarbonitrile (cis-1a) was also a substrate of the enzyme but reacted slowly. Diequatorial arrangement of the substituents in trans-1a, cis-2a, and trans-3a appears to positively influence the activity of the nitrile hydratase.