A counterselection method for Lactococcus lactis genome editing based on class IIa bacteriocin sensitivity

Research output: Contribution to journalArticle


  • Xing Wan
  • Anne M. Usvalampi
  • Per E J Saris
  • Timo M. Takala

Research units

  • University of Helsinki


In this paper, we present a new counterselection method for deleting fragments from Lactococcus lactis chromosome. The method uses a non-replicating plasmid vector, which integrates into the chromosome and makes the cell sensitive to bacteriocins. The integration vector carries pUC ori functional in Escherichia coli but not in L. lactis, an erythromycin resistance gene for selecting single crossover integrants, and two fragments from L. lactis chromosome for homologous recombinations. In addition, the integration vector is equipped with the Listeria monocytogenes gene mptC encoding the mannose-phosphotransferase system component IIC, the receptor for class IIa bacteriocins. Expression of mptC from the integration vector renders the naturally resistant L. lactis sensitive to class IIa bacteriocins. This sensitivity is then used to select the double crossover colonies on bacteriocin agar. Only the cells which have regained the endogenous bacteriocin resistance through the loss of the mptC plasmid will survive. The colonies carrying the desired deletion can then be distinguished from the wild-type revertants by PCR. By using the class IIa bacteriocins leucocin A, leucocin C or pediocin AcH as the counterselective agents, we deleted 22- and 33-kb chromosomal fragments from the wild-type nisin producing L. lactis strain N8. In conclusion, this counterselection method presented here is a convenient, efficient and inexpensive technique to generate successive deletions in L. lactis chromosome.


Original languageEnglish
Pages (from-to)9661-9669
Number of pages9
JournalApplied Microbiology and Biotechnology
Issue number22
Early online date22 Sep 2016
Publication statusPublished - Nov 2016
MoE publication typeA1 Journal article-refereed

    Research areas

  • Class IIa bacteriocin, Counterselection, Genome editing, Lactic acid bacteria

ID: 8775634