In this study, we developed two new whole-cell biocatalysts by immobilizing aminopeptidase (Aps) on the surface of yeast cells, using N-terminal fusion and C-terminal fusion through lectin mediated display system. After the two strains were cultured in the medium with galactose as inducer for 48 hours, the activity of expressing Aps was at a high level of 0.25 U/OD600/mL and 0.12 U/OD600/mL. The correct location of Aps was confirmed by immunofluorescence analysis and flow cytometry. Afterwards two whole cell catalysts could be reused with high stability as it retained more than 70% of initial activity after ten repeated batch reactions. Using β-cypermethrin (β-CP) as a substrate, the effectiveness of two new whole-cell catalysts in the treatment of highly hydrophobic organic pollutants was evaluated. The results showed that when the concentration of β-CP was 200 mg·L -1, the hydrolysis rates of the two whole cell catalysts were 33.16 μmol·L -1·day -1 and 28.99 μmol·L -1·day -1, and has the ability to degrade a variety of pyrethroid pesticides. The β-CP residue in lettuce and cherry tomatoes could be removed more than 70% under the conditions of the Aga2N-Aps whole cell catalyst preparation dilution of 100 times. This is the first report on the development of surface display Aps biocatalyst, which can be used as an effective and renewable alternative for the treatment of highly hydrophobic organic pollutants.

Deepening and expanding the understanding of cyanide-degrading enzymes are the foundation of developing new technology for cyanide bioremediation. In this study, a putative cyanide-degrading enzyme gene from Alcaligenes sp. DN25(CGMCC 5734) was cloned and expressed in Escherichia coli. The purified recombinant enzyme named as cdE, consisting of a 38-kDa polypeptide, showed 99% amino acid sequence identity with cyanidase derived from Pseudomonas stutzeri AK61. However, the cdE was supposed to have both cyanide dihydratase (CynD) and cyanide hydratase (CHT) activities based on the findings that formate, ammonium and formamide were simultaneously generated during cyanide enzymatic degradation. The enzymatic properties of cdE were characterized with an optimal activity at a temperature of 30°C, pH of 7.0, and could even maintain approximately 50% activity at pH 9.0. More importantly, the selectivity of enzymatic reaction pathway was suggested related to the conformation stability of the cdE that affected by the modifications of amino acids near the active site as well as the degradation conditions, leading to produce different ratios of formate and formamide. As far as we know, this is the first report of a cyanide-degrading enzyme possessing bifunctional catalysis activity, which might become a supplement of cyanide-degrading enzyme databases.