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Construction of a dextran-free Leuconostoc citreum mutant by targeted disruption of the dextransucrase gene

Authors

  • Q. Jin,

    1. Department of Food Science, Yanbian University, Yanji, Jilin, China
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    • Contributed equally to this work.
  • L. Li,

    1. Brain Korea 21 Center for Bio-Resource Development, Division of Animal, Horticultural, and Food Sciences, Chungbuk National University, Cheongju, Korea
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    • Contributed equally to this work.
  • Y.J. Kim,

    1. Department of Milk Processing Research Team, Korea Yakult, Youngin, Korea
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  • N.S. Han

    Corresponding author
    1. Brain Korea 21 Center for Bio-Resource Development, Division of Animal, Horticultural, and Food Sciences, Chungbuk National University, Cheongju, Korea
    • Correspondence

      Nam Soo Han, Brain Korea 21 Center for Bio-Resource Development, Division of Animal, Horticultural, and Food Sciences, Chungbuk National University, Cheongju 361-763, Korea

      E-mail: namsoo@cbnu.ac.kr

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Abstract

Aims

Leuconostoc citreum is an important lactic acid bacterium in fermented foods, but dextran production often causes undesired ropiness. To prevent this side effect, a dextran-free mutant needs to be created.

Methods and Results

Homologous recombination of the dextransucrase gene (dsrC) was conducted using a segregationally unstable plasmid, pCBM32-DSUDs. A mutant was obtained on sucrose agar medium, and a site-specific insertional inactivation in the gene was confirmed. When cultured in sucrose medium, the mutant strain produced no dextransucrase or dextran. Additionally, it showed a longer lag phase (9 h) than the wild-type strain (3 h), providing new insights into the role of dextransucrase in carbohydrate metabolism of Leuconostoc.

Conclusions

In this study, a dextransucrase knockout mutant was constructed. It was found that Leuc. citreum dextransucrase not only synthesizes dextran for cell protection but also provides fructose as an important carbon source for cell growth.

Significance and Impact of the Study

This knockout mutation was generated for the first time in Leuccitreum. The dextran-free mutant has the potential to be used for various industrial purposes, including as a starter culture for production of nonviscous fermented foods and as a dextran-free host for production of recombinant proteins.

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