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Journal of Bacteriology, November 2005, p. 7845-7852, Vol. 187, No. 22
0021-9193/05/$08.00+0     doi:10.1128/JB.187.22.7845-7852.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Alternate Sigma Factor RpoS Is Required for the In Vivo-Specific Repression of Borrelia burgdorferi Plasmid lp54-Borne ospA and lp6.6 Genes

Melissa J. Caimano,1*,{dagger} Christian H. Eggers,1,{dagger} Cynthia A. Gonzalez,1 and Justin D. Radolf1,2

Departments of Medicine,1 Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, Connecticut 060302

Received 11 July 2005/ Accepted 21 August 2005

While numerous positively regulated loci have been characterized during the enzootic cycle of Borrelia burgdorferi, very little is known about the mechanism(s) involved in the repression of borrelial loci either during tick feeding or within the mammalian host. Here, we report that the alternative sigma factor RpoS is required for the in vivo-specific repression of at least two RpoD-dependent B. burgdorferi loci, ospA and lp6.6. The downregulation of ospA and Ip6.6 appears to require either a repressor molecule whose expression is RpoS dependent or an accessory factor which enables RpoS to directly interact with the ospA and Ip6.6 promoter elements, thereby blocking transcription by RpoD. The central role for RpoS during the earliest stages of host adaptation suggests that tick feeding imparts signals to spirochetes that trigger the RpoS-dependent repression, as well as expression, of in vivo-specific virulence factors critical for the tick-to-mammalian host transition.

* Corresponding author. Mailing address: Department of Medicine, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030-3715. Phone: (860) 679-8390. Fax: (860) 679-1358. E-mail: mcaima{at}up.uchc.edu.

{dagger} M.J.C. and C.H.E. contributed equally to this work.

Journal of Bacteriology, November 2005, p. 7845-7852, Vol. 187, No. 22
0021-9193/05/$08.00+0     doi:10.1128/JB.187.22.7845-7852.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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