The complete genome sequence of Lactobacillus bulgaricus reveals extensive and ongoing reductive evolution

Proc Natl Acad Sci U S A. 2006 Jun 13;103(24):9274-9. doi: 10.1073/pnas.0603024103. Epub 2006 Jun 5.


Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) is a representative of the group of lactic acid-producing bacteria, mainly known for its worldwide application in yogurt production. The genome sequence of this bacterium has been determined and shows the signs of ongoing specialization, with a substantial number of pseudogenes and incomplete metabolic pathways and relatively few regulatory functions. Several unique features of the L. bulgaricus genome support the hypothesis that the genome is in a phase of rapid evolution. (i) Exceptionally high numbers of rRNA and tRNA genes with regard to genome size may indicate that the L. bulgaricus genome has known a recent phase of important size reduction, in agreement with the observed high frequency of gene inactivation and elimination; (ii) a much higher GC content at codon position 3 than expected on the basis of the overall GC content suggests that the composition of the genome is evolving toward a higher GC content; and (iii) the presence of a 47.5-kbp inverted repeat in the replication termination region, an extremely rare feature in bacterial genomes, may be interpreted as a transient stage in genome evolution. The results indicate the adaptation of L. bulgaricus from a plant-associated habitat to the stable protein and lactose-rich milk environment through the loss of superfluous functions and protocooperation with Streptococcus thermophilus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Base Sequence*
  • Carbohydrate Metabolism
  • Evolution, Molecular*
  • Genome, Bacterial*
  • Interspersed Repetitive Sequences
  • Lactobacillus delbrueckii / genetics*
  • Lactobacillus delbrueckii / metabolism
  • Molecular Sequence Data
  • Sequence Analysis, DNA
  • Streptococcus thermophilus / metabolism
  • Synteny
  • Yogurt / microbiology


  • Bacterial Proteins