Nitrilases are important industrial enzymes that convert nitriles directly into the corresponding carboxylic acids. In the current work, the fragment with a length of 1068 bp that encodes the A. faecalis ZJUTB10 nitrilase was obtained. Moreover, a catalytic triad was proposed and verified by site-directed mutagenesis, and the detailed mechanism of this nitrilase was clarified. The substrate specificity study demonstrated that the A. faecalis ZJUTB10 nitrilase belongs to the family of arylacetonitrilases. The optimum pH and temperature for the purified nitrilase was 7-8 and 40 °C, respectively. Mg(2+) stimulated hydrolytic activity, whereas Cu(2+), Co(2+), Ni(2+), Ag(+), and Hg(2+) showed a strong inhibitory effect. The K(m) and v(max) for mandelonitrile were 4.74 mM and 15.85 μmol min(-1) mg(-1) protein, respectively. After 30 min reaction using the nitrilase, mandelonitrile at the concentration of 20 mM was completely hydrolyzed and the enantiomeric excess against (R)-(-)-mandelic acid was >99%. Characteristics investigation indicates that this nitrilase is promising in catalysis applications.

Bacterial strain ZJB-09211 capable of amidase production has recently been isolated from soil samples. The strain is able to asymmetrically hydrolyze l-tryptophanamide from d,l-tryptophanamide to produce l-tryptophan in high yield and with excellent stereoselectivity (enantiomeric excess > 99.9 %, and enantiomeric ratio > 200). Strain ZJB-09211 has been identified as Flavobacterium aquatile based on the cell morphology analysis, physiological tests, and the 16S rDNA sequence analysis. Optimization of the fermentation medium led to an about six-fold increase in the amidase activity of strain ZJB-09211, which reached 501.5 U L−1. Substrate specifity and stereoselectivity investigations revealed that amidase of F. aquatile possessed a broad substrate spectrum and high enantioselectivity.

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