Reciprocal Expression of ospA and ospC in Single Cells of Borrelia burgdorferi

Outer surface proteins (Osp) A and C of the Lyme disease spirochete (Borrelia burgdorferi ) are selectively produced and of functional significance in the tick vector and mammalian host, respectively. Some studies indicate a simple, reciprocal relationship where the signals and pathways that turn onospC also turn offospA . Other studies indicate a more complex regulation where many spirochetes produce both proteins and others produce one of the proteins or neither protein. Here, we have used flow cytometry to characterizeospA andospC transcript and protein levels in individual bacterial cells grown in culture. The results support a simple, reciprocal model where, at the level of single cells, the transcription ofospC is linked to the repression ofospA . We also demonstrate that under conditions conducive for OspC production, spirochetes display an “all or none” response, with some cells displaying high levels ofospC transcription and others demonstrating little or no transcription. Despite the reciprocal regulation ofospA andospC at the single-cell level, we propose that spirochetes display an array of phenotypes due to stochasticity in the pathways that regulateosp expression and the slow turnover of outer surface proteins.