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Infect. Immun. doi:10.1128/IAI.00714-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Tightly Regulated Surface Protein of Borrelia burgdorferi is Not Essential to the Mouse-Tick Infectious Cycle

Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 903 South 4th St., Hamilton, Montana 59840

^* To whom correspondence should be addressed. Email: pestewart{at}niaid.nih.gov.

	Abstract

Borrelia burgdorferi synthesizes a variety of differentially regulated outer surface lipoproteins in the tick vector and in vertebrate hosts. Among these is OspD, a protein that is highly induced in vitro by conditions that mimic the tick environment. Using genetically engineered strains deleted for ospD, we demonstrate that this protein is not required for B. burgdorferi survival and infectivity in either the mouse or tick. However, examination of both transcript levels and protein expression indicates that OspD expression is limited to a discrete window of time during B. burgdorferi replication within the tick. This timeframe corresponds to tick detachment from the host following feeding, and expression of OspD continues during the tick digestion of the bloodmeal, but is low or undetectable after the tick has molted. The high level of OspD production correlates to the highest cell densities that B. burgdorferi is known to reach in vivo. Although non-essential to the infectious cycle of B. burgdorferi, the tight regulation of expression suggests a beneficial contribution of OspD to the spirochete during bacterial replication within the tick midgut.