Jingcong Xie

Overexpression and characterization of laccase from Trametes versicolor in Pichia pastoris

AbstarctA laccase-encoding gene of Trametes versicolor, lccA, was cloned and expressed in Pichia pastoris X33. The lccA gene consists of a 1560 bp open reading frame encoding 519 amino acids, which was classified into family copper blue oxidase. To improve the expression level of recombinant laccase in P. pastoris, conditions of the fermentation were optimized by the single factor experiments. The optimal fermentation conditions for the laccase production in shake flask cultivation using BMGY medium were obtained: the optimal initial pH 7.0, the presence of 0.5 mM Cu2+, 0.6% methanol added into the culture every 24 h. The laccase activity was up to 11, 972 U/L under optimal conditions after 16 days of induction in a medium with 4% peptone. After 100 h of large scale production in 5 L fermenter the enzyme activity reached 18, 123 U/L. The recombinant laccase was purified by ultrafiltration and (NH4)2SO4 precipitation showing a single band on SDS-PAGE, which had a molecular mass of 58 kDa. The optimum pH and temperature for the laccase were pH 2.0 and 50°C with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a substrate. The recombinant laccase was stable over a pH range of 2.0–7.0. The Km and the Vmax value of LccA were 0.43 mM and 82.3 U/mg for ABTS, respectively.

Characterization of a novel arabinose-tolerant α-L-arabinofuranosidase with high ginsenoside Rc to ginsenoside Rd bioconversion productivity.

(i) To investigate the enzymatic characterization of α‐l‐arabinofuranosidase from Thermotoga thermarum DSM5069. (ii) To evaluate the performance of its excellent properties on converting ginsenoside Rc to ginsenoside Rd.

High-level expression of recombinant thermostable β-glucosidase in Escherichia coli by regulating acetic acid

In the fermentation progress, fermentation parameters including the feed rate, induction temperature, and induction pH evidently regulate the accumulation of acetic acid generated by recombinant E. coli in the medium. The production of thermostable β-glucosidase (Tpebgl3) was increased by optimizing the parameters mentioned step by step. The optimal conditions were obtained with the highest enzyme expression (560.4U/mL) and the maximum DCW (65g/L) at the pre-induction specific growth rate of 0.2h-1 followed by a post-induction specific growth rate (0.18h-1); induction temperature is 39°C; the pH is 7.2; the concentration of acetic acid was maintained all along below 0.9g/L. Results show it is necessary for the synthesis of Tpebgl3 to regulate the accumulation of acetic acid at the premise of feeding to meet the normal growth of E. coli. The production of Tpebgl3 by recombinant E. coli is the highest reported to date.