Simultaneous Coexpression ofBorrelia burgdorferiErp Proteins Occurs through a Specific,erpLocus-Directed Regulatory Mechanism

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Abstract
An individualBorrelia burgdorferibacterium can encode as many as 13 different Erp (OspE/F-related) proteins from mono-and bicistronic loci that are carried on up to 10 separate plasmids. We demonstrate through multilabel immunofluorescence analyses that individual bacteria simultaneously coexpress their entire Erp protein repertoire. While it has been proposed thatB. burgdorfericontrols expression of Erp and other plasmid-encoded proteins through changes in DNA topology, we observed regulated Erp expression in the absence of detectable differences in DNA supercoiling. Likewise, inhibition of DNA gyrase had no detectable effect on Erp expression. Furthermore, expression of loci physically adjacent toerploci was observed to be independently regulated. It is concluded that Erp expression is regulated by a mechanism(s) directed aterploci and not by a global, plasmid-wide mechanism.