A specific mutation in the promoter region of the silent cel cluster accounts for the appearance of lactose-utilizing Lactococcus lactis MG1363

Appl Environ Microbiol. 2012 Aug;78(16):5612-21. doi: 10.1128/AEM.00455-12. Epub 2012 Jun 1.


The Lactococcus lactis laboratory strain MG1363 has been described to be unable to utilize lactose. However, in a rich medium supplemented with lactose as the sole carbon source, it starts to grow after prolonged incubation periods. Transcriptome analyses showed that L. lactis MG1363 Lac(+) cells expressed celB, encoding a putative cellobiose-specific phosphotransferase system (PTS) IIC component, which is normally silent in MG1363 Lac(-) cells. Nucleotide sequence analysis of the cel cluster of a Lac(+) isolate revealed a change from one of the guanines to adenine in the promoter region. We showed here that one particular mutation, taking place at increased frequency, accounts for the lactose-utilizing phenotype occurring in MG1363 cultures. The G-to-A transition creates a -10 element at an optimal distance from the -35 element. Thus, a fully active promoter is created, allowing transcription of the otherwise cryptic cluster. Nuclear magnetic resonance (NMR) spectroscopy results show that MG1363 Lac(+) uses a novel pathway of lactose utilization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon / metabolism
  • Culture Media / chemistry
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • Gene Expression Profiling
  • Lactococcus lactis / genetics*
  • Lactococcus lactis / growth & development
  • Lactococcus lactis / metabolism*
  • Lactose / metabolism*
  • Point Mutation*
  • Promoter Regions, Genetic*
  • Sequence Analysis, DNA
  • Transcriptome


  • Culture Media
  • DNA, Bacterial
  • Carbon
  • Lactose