Yunhe Cao

Directed evolution of a β-1,3-1,4-glucanase from Bacillus subtilis MA139 for improving thermal stability and other characteristics.

In order to improve some characteristics of a β‐1,3‐1,4‐glucanase from Bacillus subtilis MA139, directed evolution was conducted in this study. After error‐prone PCR, the β‐1,3‐1,4‐glucanase gene, glu‐opt, was cloned into the vector pBGP1 and transformed into Pichia pastoris X‐33 to construct a mutant library. Three variants named as 7‐32, 7‐87, and 7‐115 were screened from 8000 colonies. Amino‐acid sequence analysis showed that these mutants had one or two amino‐acid substitutions (7‐32: T113S, 7‐87: M44V/N53H, and 7‐115: N157D). The variants were over‐expressed in P. pastoris by methanol induction. After purification of the enzyme proteins, the characteristics of the variants were analyzed in detail. It indicated that these mutant enzymes had broader ranges of pH value and better pH stability than the wild‐type enzyme. The mutant enzyme 7‐87 had the best ability to tolerate an acid environment (pH 2.0), while the wild‐type enzyme had no activity under this condition. Moreover, all these mutants demonstrated improved thermal stability. In particular, the mutant enzyme 7‐32 had residual enzymatic activity of 60% and 40% after being incubated at 80 °C and 90 °C for 10 min. While, the wild‐type enzyme had no residual enzymatic activity after being incubated at 80 °C for 4 min. In addition, the mutant enzymes had better tolerance to some chemicals than the wild‐type enzyme. The improved stability could enhance the prospects for this enzyme to have use in the feed industry to reduce the effects of the anti‐nutritional factor β‐glucan.

Improved thermostability of an acidic xylanase from Aspergillus sulphureus by combined disulphide bridge introduction and proline residue substitution

As a feed additive, xylanase has been widely applied in the feed of monogastric animals, which contains multiple plant polysaccharides. However, during feed manufacture, the high pelleting temperatures challenge wild-type xylanases. The aim of this study was to improve the thermostability of Aspergillus sulphureus acidic xylanase. According to the predicted protein structure, a series of disulphide bridges and proline substitutions were created in the xylanase by PCR, and the mutants were expressed in Pichia pastoris. Enzyme properties were evaluated following chromatographic purification. All the recombinant enzymes showed optima at pH 3.0 and 50 °C or 55 °C and better resistance to some chemicals except for CuSO4. The specific activity of the xylanase was decreased by introduction of the mutations. Compared to the wild-type enzyme, a combined mutant, T53C-T142C/T46P, with a disulphide bond at 53–142 and a proline substitution at 46, showed a 22-fold increase of half-life at 60 °C. In a 10-L fermentor, the maximal xylanase activity of T53C-T142C/T46P reached 1,684 U/mL. It was suggested that the T53C-T142C/T46P mutant xylanase had excellent thermostability characteristics and could be a prospective additive in feed manufacture.

Cloning and functional expression of α -galactosidase cDNA from Penicillium janczewskii zaleski

In recent years, α-galactosidase has been attracting more and more attention because of its potential applications in many aspects. Using reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends, a full-length cDNA sequence composed of 2,439 bp was cloned from Penicillium janczewskii zaleski and was subcloned into pPICZαA and transformed into Pichia pastoris strain X-33. In a 10-L fermentor, the recombinant yeast expressed α-galactosidase with a yield of 254 U/mL by methanol induction for 120 h. The recombinant enzyme showed the optimal activity at 40°C and pH 5.2. The Km values of the recombinant enzyme using p-nitrophenyl-α-D-galactopyranoside (pNPG), melibiose, raffinose and stachyose as substrates were 1, 16, 17.8 and 5.3 mM, respectively. Vmax values were 227.3, 116.7, 104.8, and 80.6 μM/min using pNPG, melibiose, raffinose and stachyose as substrates, respectively. The α-galactosidase exhibited no sensitivity to various metal ions and ethylenediaminetetraacetic acid, and hydrolyzed melibiose, raffinose and stachyose with different levels of galactose release. The biochemical characteristics of the α-galactosidase suggest that the enzyme may have a prospective application in feed industry as an additive.

Codon optimization, expression and characterization of Bacillus subtilis MA139 β-1,3-1,4-glucanase in Pichia pastoris

Abstractβ-1,3-1,4-Glucanase has been broadly used in feed and brewing industries. According to the codon bias of Pichia pastoris, the Bacillus subtilis MA139 β-1,3-1,4-glucanase gene was de novo synthesized and expressed in P. pastoris X-33 strain under the control of the alcohol oxidase 1 promoter. In a 10-L fermentor, the β-1,3-1,4-glucanase was overexpressed with a yield of 15,000 U/mL by methanol induction for 96 h. The recombinant β-1,3-1,4-glucanase exhibited optimal activity at 40°C and pH 6.4. The activity of the recombinant β-1,3-1,4-glucanase was not significantly affected by various metal ions and chemical reagents. To our knowledge, the expression of this β-1,3-1,4-glucanase from Bacillus sp. in P. pastoris is in relatively high level compared to previous reports. These biochemical characteristics suggest that the recombinant β-1,3-1,4-glucanase has a prospective application in feed and brewing industries.

In-fusion expression and characterization of β-xylanase and β-1,3-1,4-glucanase in Pichia pastoris

Two chimeric genes, XynA-Bs-Glu-1 and XynA-Bs-Glu-2, encoding Aspergillus sulphureus β-xylanase (XynA, 26 kDa) and Bacillus subtilis β-1,3-1,4-glucanase (Bs-Glu, 30 kDa), were constructed via in-fusion by different linkers and expressed successfully in Pichia pastoris. The fusion protein (50 kDa) exhibited both β-xylanase and β-1,3-1,4-glucanase activities. Compared with parental enzymes, the moiety activities were decreased in fermentation supernatants. Parental XynA and Bs-Glu were superior to corresponding moieties in each fusion enzymes because of lower Kn higher kcat. Despite some variations, common optima were generally 50°C and pH 3.4 for the XynA moiety and parent, and 40°C and pH 6.4 for the Bs-Glu counterparts. Thus, the fusion enzyme XynA-Bs-Glu-1 and XynA-Bs-Glu-2 were bifunctional.

Effects of xylanase supplementation to wheat-based diets on growth performance, nutrient digestibility and gut microbes in weanling pigs

Objective This study was designed to investigate the effects of an Aspergillus sulphureus xylanase expressed in Pichia pastoris on the growth performance, nutrient digestibility and gut microbes in weanling pigs. Methods A total of 180 weanling pigs (initial body weights were 8.47±1.40 kg) were assigned randomly to 5 dietary treatments. Each treatment had 6 replicates with 6 pigs per replicate. The experimental diets were wheat based with supplementation of 0, 500, 1,000, 2,000, and 4,000 U xylanase/kg. The experiment lasted 28 days (early phase, d 0 to 14; late phase, d 15 to 28). Results In the early phase, compared to the control, average daily gain (ADG) was higher for pigs fed diets supplemented with xylanase and there was a quadratic response in ADG (p<0.05). In the entire phase, ADG was higher for the pigs fed 1,000 or 2,000 U/kg xylanase compared to the control (p<0.05). The gain to feed ratio was higher for pigs fed diets supplemented with 1,000 or 2,000 U/kg xylanase compared to the control (p<0.05). Increasing the amount of xylanase improved the apparent total tract digestibility of dry matter, crude protein, neutral detergent fiber, calcium, and phosphorus during both periods (p<0.05). Xylanase supplementation (2,000 U/kg) decreased the proportion of Lachnospiraceae (by 50%) in Firmicutes, but increased Prevotellaceae (by 175%) in Bacteroidetes and almost diminished Enterobacteriaceae (Escherichia-Shigella) in Proteobacteria. Conclusion Xylanase supplementation increased growth performance and nutrient digestibility up to 2,000 U/kg. Supplementation of xylanase (2,000 U/kg) decreased the richness of gut bacteria but diminished the growth of harmful pathogenic bacteria, such as Escherichia-Shigella, in the colon.