The life transmission cycle of B. burgdorferi requires migration of spirochetes from tick's gut to its salivary glands during vertebrate's blood sucking, penetrating to the vertebrate's tissues and their colonization. A special feature of these bacteria, despite its relatively small genome, is the ability to adapt in different host environments. These unusual properties of borreliae are associated with large number of plasmids, which show a high variability as a result of recombination with each other. Changes in the synthesis of outer proteins are the first strategy of borreliae in avoiding the destructive effect of the host's immune system. Then, by colonizing tissues, they initiate production of Erp and CRASP proteins, which bind regulators and components of complement and repress the cytolytic effect of the host's serum. Some evidences indicate that the spirochetes use quorum sensing as a mechanism to control protein expression. B. burgdorferi probably utilizes a LuxS/autoinducer-2-dependent quorum sensing mechanism. However, it is not yet known how B. burgdorferi detect AI-2. Analysis of the results of expression studies of the luxS gene shows that the molecular mechanisms of this phenomenon in B. burgdorferi are only fragmentarily known. Continuation of quorum sensing studies may be essential in improving the construction of vaccines as well as therapy of Lyme disease.