Expression of Borrelia burgdorferi erp genes during infection of non-human primates Jennifer C. Miller a , Kavitha Narayan b , Brian Stevenson a, * , Andrew R. Pachner b a Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, MS 415 Chandler Medical Center, Lexington, KY 40536-0298, USA b Department of Neurology and Neuroscience, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, 185 S. Orange Avenue, Newark, NJ 07103, USA Received 14 February 2005; received in revised form 13 April 2005; accepted 14 April 2005 Available online 20 June 2005 Abstract All examined isolates of the Lyme disease spirochete contain multiple operons encoding Erp outer membrane lipoproteins. Many Erp proteins have been demonstrated to bind the host complement regulator factor H, and may thereby help protect the bacteria from complement-mediated killing during mammalian infection. Consistent with that hypothesis, all Erp proteins are produced by Borrelia burgdorferi during transmission between tick vectors and mammalian hosts. The present study examined whether erp genes are also expressed by B. burgdorferi following establishment of mammalian infection. To that end, quantitative RT-PCR was utilized to assess erp transcription levels within different tissues of infected non-human primates, a model that closely mimics human Lyme disease. The majority of erp genes were detectably transcribed after more than 3 months of mammalian infection. Intriguingly, differences in expression levels were noted among the various erp loci. No significant differences in erp expression were apparent between examined tissues, which included central and peripheral nervous system tissue, skeletal muscle, bladder, skin and heart tissues. These data strongly suggest that Erp proteins are expressed by B. burgdorferi throughout infection of their vertebrate hosts. q 2005 Elsevier Ltd. All rights reserved. Keywords: Borrelia burgdorferi; Lyme disease; Genes 1. Introduction Lyme disease is the most commonly reported vector- borne illness affecting humans in the United States, Europe and many other parts of the Earth, and is caused by the spirochete Borrelia burgdorferi sensu lato [1]. This bacterium is maintained in nature by cycling between hard ticks of the genus Ixodes and warm blooded vertebrates. In order for the bacteria to establish infection, disseminate, and persist within those two very different types of hosts, B. burgdorferi must regulate the expression of numerous genes and proteins. Among the B. burgdorferi proteins known to be differentially expressed during the natural tick-mammal infectious cycle are the Erp outer surface lipoproteins [2–13]. erp genes have been identified in every examined Lyme disease spirochete isolate, strongly suggesting that the Erp proteins perform a function(s) vital to B. burgdorferi [3,6,11,13–18]. Individual B. burgdorferi may contain upwards of six separate erp loci, each of which is located on a member of the cp32 family of circular plasmid-like prophages [16,19–22]. Loci may be either mono- or bicistronic operons, and all bicistronic erps are co- transcribed [3,7,14]. In addition, all erp genes are preceded by highly similar promoter regions that bind the same DNA- binding protein(s), and are regulated by both temperature and as-yet unidentified chemical signals [2,3,6–8,11,12,17, 23,24]. In the B. burgdorferi type strain, B31, erp mRNAs and Erp proteins are simultaneously co-expressed by bacteria both during cultivation and within the midguts of feeding ticks [5,25,26]. However, some incidences of apparent asynchrony in erp gene expression have been observed, probably reflecting variations in locus promoter Microbial Pathogenesis 39 (2005) 27–33 www.elsevier.com/locate/micpath 0882-4010/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.micpath.2005.04.001 * Corresponding author. Tel.: C1 859 257 9358; fax: C1 859 257 8994. E-mail address: bstev0@uky.edu (B. Stevenson).