title: Increase of stress resistance in Lactococcus lactis via a novel food-grade vector expressing a shsp gene from Streptococcus thermophilus.
abstract: The effects of the expression of a small heat shock protein (shsp) gene from Streptococcus thermophilus on stress resistance in Lactococcus lactis under different environmental stresses were investigated in this study. pMG36e-shsp, an expression vector, was first constructed by inserting a shsp open reading frame (ORF) cloned from S. thermophilus strain St-QC into pMG36e. Then, a food-grade expression vector, pMG-shsp, was generated by deleting the erythromycin resistance gene from pMG36e-shsp. The transformation rate of pMG-shsp was comparable to that of pMG36e-shsp when each of these two vectors was introduced into L. lactis. These results demonstrated that the shsp ORF could successfully used as a food-grade selection marker in both pMG-shsp and pMG36e-shsp. Furthermore, the growth characteristics were almost the same between L. lactis ML23 transformants harboring pMG36e or pMG-shsp. The survival rate of L. lactis ML23 expressing the shsp ORF were increased to 0.032%, 0.006%, 0.0027%, 0.03%, and 0.16% under the following environmental stresses: heat, acid, ethanol, bile salt and H2O2, respectively. These results indicated that the expression of the shsp gene in the food-grade vector pMG-shsp conferred resistance to environmental stresses without affecting the growth characteristics of L. lactis ML23.
authors.affiliation: College of Food Science and Technology, Agricultural University of Hebei , Baoding, 071001 , china ; College of Food Science and Nutritional Engineering, China Agricultural University , Beijing, 100083 , China.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Tian
authors.forename: Jianxin
authors.initials: J
authors.lastname: Tan
authors.forename: Lifang
authors.initials: L
authors.lastname: Zhang
authors.forename: Xinxi
authors.initials: X
authors.lastname: Gu
authors.forename: Wentao
authors.initials: W
authors.lastname: Xu
authors.forename: Xinghua
authors.initials: X
authors.lastname: Guo
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Luo
keywords: Lactococcus lactis; Streptococcus thermophilus; food-grade vector; shsp gene; stress resistance
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