Nitrile- and amide-hydrolysing activity of acrylic acid-tolerant yeast Trichosporon asahii ZZB-1

An ammonia acrylate-tolerant yeast ZZB-1, capable of nitrile- and amide-hydrolysing activity, was isolated from soil samples. Based on the morphology, 18S rRNA gene, internal-transcribed-spacer and 26S rRNA gene D1/D2 domain sequences, this strain was provisionally identified as Trichosporon asahii. Strain ZZB-1 contained a two-enzyme system, i.e. nitrile-hydrolysing and amide-hydrolysing activity for the hydrolysis of nitriles/amides to corresponding acids and ammonia. The nitrile-hydrolysing activity was weakly constitutively produced by the resting cells of T. asahii ZZB-1. The addition of phenylacetonitrile, acrylamide and acrylic acid significantly enhanced this hydrolysis. The cells of T. asahii ZZB-1 also exhibited weakly constitutive amide-hydrolysing activity with an affinity for acrylamide (1.47 U), and this activity clearly increased to 50.29, 51.82 and 13.59 U for acrylamide, acetamide, and benzamide, respectively, in the presence of 1% acrylic acid (v/v) during cultivation. The amide-hydrolysing activity of T. asahii ZZB-1 was inactivated at 40°C. The cationic metals Ca2+, Zn2+, and Mn2+ had a significant positive effect on the amide-hydrolysing activity of T. asahii ZZB-1, but Co2+ and Cu2+ had a significant negative effect. The resting cells of T. asahii ZZB-1 achieved high amide-hydrolysing activity of 78.87 U (μmol/min/g, dry cell weight) at under optimum conditions (35°C, pH 9.5, 1 mM Zn2+).