Global Analysis of Borrelia burgdorferi Genes Regulated by Mammalian Host-Specific Signals

Abstract

Lyme disease is a tick-borne infection that can lead to chronic, debilitating problems if not recognized or treated appropriately. Borrelia burgdorferi, the causative agent of Lyme disease, is maintained in nature by a complex enzootic cycle involving Ixodes ticks and mammalian hosts. Many previous studies support the notion that B. burgdorferi differentially expresses numerous genes and proteins to help it adapt to growth in the mammalian host. In this regard, several studies have utilized a dialysis membrane chamber (DMC) cultivation system to generate "mammalian host-adapted" spirochetes for the identification of genes selectively expressed during mammalian infection. Here, we have exploited the DMC cultivation system in conjunction with microarray technology to examine the global changes in gene expression that occur in the mammalian host. To identify genes regulated by only mammal-specific signals and not by temperature, borrelial microarrays were hybridized with cDNA generated either from organisms temperature shifted in vitro from 23°C to 37°C or from organisms cultivated by using the DMC model system. Statistical analyses of the combined data sets revealed that 125 genes were expressed at significantly different levels in the mammalian host, with almost equivalent numbers of genes being up-or down-regulated by B. burgdorferi within DMCs compared to those undergoing temperature shift. Interestingly, during DMC cultivation, the vast majority of genes identified on the plasmids were down-regulated (79%), while the differentially expressed chromosomal genes were almost entirely upregulated (93%). Global analysis of the upstream promoter regions of differentially expressed genes revealed that several share a common motif that may be important in transcriptional regulation during mammalian infection. Among genes with known or putative functions, the cell envelope category, which includes outer membrane proteins, was found to contain the most differentially expressed genes. The combined findings have generated a subset of genes that can now be further characterized to help define their role or roles with regard to B. burgdorferi virulence and Lyme disease pathogenesis.Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most common arthropod-borne infection in the United States (39). Undiagnosed infection with B. burgdorferi often results in chronic disease, which can lead to sequelae such as carditis, arthritis, and neuritis (53). In nature, B. burgdorferi is maintained through a complex enzootic cycle involving ticks and mammalian hosts, typically small rodents (29). To perpetuate this enzootic cycle, B. burgdorferi must adapt physiologically to two dramatically different environments. Consistent with the adaptation process, several genes and the proteins they encode have been shown to be specifically up-regulated or down-regulated as this organism is transmitted from its tick vector to the mammalian host (1, 2, 18, 21, 23, 47). The bestcharacterized example of differential gene expression in B...

Quantitative analysis of Borrelia burgdorferi gene expression in naturally (tick) infected mouse strains

“…This complements the previous notion that from 16 identified lp54-encoded genes all but one, i.e. bba64, were down-regulated by mammalian host-specific signals, as revealed by an in vivo study using a membrane cultivation chamber [6].…”

bptA(bbe16) is essential for the persistence of the Lyme disease spirochete,Borrelia burgdorferi, in its natural tick vector

“…Previous microarray analyses performed on Bb have revealed a large number of differentially regulated genes whose functional annotations remain largely unknown (15,41,42). Whereas many of these differentially regulated genes likely represent physiological ''housekeeping'' genes typically not thought of as virulenceassociated, others have been noted in separate studies to encode virulence factors essential for Bb's infection of or survival within its arthropod or mammalian hosts (6,7,33,(43)(44)(45).…”

Relapsing fever spirochaetes produce a serine protease that provides resistance to oxidative stress and killing by neutrophils

“…The bhpA ORF is flanked by ORFs coding a thymidine kinase and a homologue of FtsH. B. burgdorferi expresses this thymidine kinase gene in mammals and its expression is regulated by the stress response sigma factor, sigma (S) (Brooks et al, 2003;Fisher et al, 2005). FtsH is an ATP-dependent Zn-protease involved in the bacterial stress response and heat shock control (Kirchner et al, 2000).…”