Shumei Fang,Xuejiao An,Hongyuan Liu,Yi Cheng,Ning Hou,Lu Feng,Xinning Huang,Chunyan Li
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 t 1/2 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.
Tannic-acid-templated magnetic mesoporous silica nanoparticles (TA-MMSNs) were synthesized for the first time. The TA-MMSNs were monodisperse spherical particles with a diameter of around 250 nm and a magnetization saturation value of 35.26 emu/g. The specific surface area of TA-MMSNs was 423.4 m 2 /g, and the diameter and cumulative volume of the pores were 9.349 nm and 1.071 cm 3 /g, respectively. The TA-MMSNs were used to prepare immobilized NHase (CLNHAs@TA-MMSNs) by forming cross-linked nitrile hydratase aggregates (CLNHAs) in pores of TA-MMSNs using glutaraldehyde as a cross-linker. CLNHAs@TA-MMSNs and free NHase had the same optimum pH (pH 7), and the optimum temperature of CLNHAs@TA-MMSNs (40 °C) was higher than that of free NHase (30 °C). Compared with free NHase, CLNHAs@TA-MMSNs exhibited improved thermal, pH, mechanical and storage stability. Furthermore, CLNHAs@TA-MMSNs was applied in production of nicotinamide, and yield of nicotinamide could reach more than 98%. The tolerance of CLNHAs@TA-MMSNs to high concentration of substrate was better than that of free NHase, and yield of nicotinamide could still reach 29.74% after seven cycles of reaction. The kinetic parameters were investigated and the results indicated a lower substrate affinity and catalytic efficiency of CLNHAs@TA-MMSNs in comparison with free NHase. This work demonstrated that TA-MMSNs could be efficiently employed as supports for enzyme immobilization.
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