Construction of first-generation lactococcal integrative cloning vectors

Area of Science:

• Microbiology
• Molecular Biology
• Genetic Engineering

Background:

• Lactococcus lactis is a key bacterium in dairy fermentation.
• Developing stable genetic tools for L. lactis is crucial for strain improvement and functional studies.
• Existing methods for genetic manipulation in L. lactis can be limited in efficiency and stability.

Purpose of the Study:

• To develop novel integrative cloning vectors for Lactococcus lactis subsp. lactis LM0230.
• To demonstrate the stable integration and expression of antibiotic resistance genes using these vectors.
• To assess the applicability of these vectors across different Lactococcus lactis strains.

Main Methods:

• Random cloning of a HindIII-digested chromosomal fragment from L. lactis LM0230.
• Dideoxy DNA sequencing to characterize the cloned fragment (1026 bp).
• Southern hybridization to confirm vector applicability.
• Insertion of erythromycin (eryr) and nisin (nisr) resistance genes into the vector.
• Integration into L. lactis LM0230 chromosome via Campbell-like and replacement recombination.
• Stability testing of integrated genes over 200 generations.

Main Results:

• Successfully developed first-generation lactococcal integrative cloning vectors.
• Confirmed stability of integrated erythromycin and nisin resistance genes in L. lactis transformants.
• Demonstrated vector applicability to other L. lactis strains, including L. lactis subsp. cremoris.
• Observed potential amplification of the integrated nisin resistance gene in transformants.

Conclusions:

• The developed integrative vectors provide a stable and applicable tool for genetic manipulation in Lactococcus lactis.
• Stable integration of antibiotic resistance genes is achievable, facilitating selection and further genetic studies.
• The potential for gene amplification warrants further investigation for applications like enhanced production.