LuxS-mediated quorum sensing in Borrelia burgdorferi, the lyme disease spirochete

Abstract

The establishment of Borrelia burgdorferi infection involves numerous interactions between the bacteria and a variety of vertebrate host and arthropod vector tissues. This complex process requires regulated synthesis of many bacterial proteins. We now demonstrate that these spirochetes utilize a LuxS/autoinducer-2 (AI-2)-based quorum-sensing mechanism to regulate protein expression, the first system of cell-cell communication to be described in a spirochete. The luxS gene of B. burgdorferi was identified and demonstrated to encode a functional enzyme by complementation of an Escherichia coli luxS mutant. Cultured B. burgdorferi responded to AI-2 by altering the expression levels of a large number of proteins, including the complement regulator factor H-binding Erp proteins. Through this mechanism, a population of Lyme disease spirochetes may synchronize production of specific proteins needed for infection processes.

FIG. 1.

Alignment of the predicted amino acid sequences of the LuxS proteins of B. burgdorferi (Bb) and V. harveyi (Vh). Residues predicted to be involved in LuxS function are indicated by asterisks (30, 54).

FIG. 2.

Results of bioassays of AI-2 activity, reported as the percentage of V. harveyi BB120 control supernatant after 2 h of incubation. Averages of five assays are reported, with range bars indicating high and low extremes. Plasmid pBLS563 encodes the B. burgdorferi LuxS enzyme.

FIG. 3.

Effects of AI-2 on B. burgdorferi protein expression. Arrowheads indicate representative proteins whose expression was either increased or decreased in response to AI-2-containing supernatant. Note that the levels of a large number of proteins were altered by AI-2; at least 30 ³⁵S-labeled proteins were affected by AI-2 in bacteria cultured at 23°C, and 25 ³⁵S-labeled proteins were affected in bacteria grown at 34°C.

FIG. 3.

Effects of AI-2 on B. burgdorferi protein expression. Arrowheads indicate representative proteins whose expression was either increased or decreased in response to AI-2-containing supernatant. Note that the levels of a large number of proteins were altered by AI-2; at least 30 ³⁵S-labeled proteins were affected by AI-2 in bacteria cultured at 23°C, and 25 ³⁵S-labeled proteins were affected in bacteria grown at 34°C.

FIG. 4.

Effects of added AI-2 on the expression of specific proteins by B. burgdorferi. Bacteria were cultivated in BSK-H medium containing either control cell-free E. coli supernatant (−) or BSK-H containing supernatant with AI-2 (+) and then lysed and analyzed by immunoblot with monoclonal antibodies specific for ErpA/I/N or OspC.