BB0844, an RpoS-Regulated Protein, Is Dispensable for Borrelia burgdorferi Infectivity and Maintenance in the Mouse-Tick Infectious Cycle

Abstract

The genome of Borrelia burgdorferi, the causative agent of Lyme disease, is comprised of a large linear chromosome and numerous smaller linear and circular plasmids. B. burgdorferi exhibits substantial genomic variation, and previous studies revealed genotype-specific variation at the right chromosomal telomere. A correlation has also been established between genotype and invasiveness. The correlation between chromosome length and genotype and between genotype and invasiveness suggested that a gene(s) at the right chromosome telomere may be required for virulence. Of particular interest was bb0844, an RpoS-regulated gene at the right telomere, the expression of which is induced when the spirochete undergoes adaptation to the mammalian host. The structure of the right chromosomal telomere was examined in 53 B. burgdorferi clinical isolates of various genotypes. Four distinct patterns were observed for bb0844: (i) chromosomal localization, (ii) plasmid localization, (iii) presence on both chromosome and plasmid, and (iv) complete absence. These patterns correlated with the B. burgdorferi genotype. On the basis of available sequence data, we propose a mechanism for the genomic rearrangements that accounts for the variability in bb0844 genomic localization. To further explore the role of BB0844 in the spirochete life cycle, a bb0844 deletion mutant was constructed by allelic exchange, and the viability of wild-type and bb0844 deletion mutants was examined in an experimental mouse-tick infection model. The bb0844 mutant was fully infectious in C3H/HeJ mice by either needle inoculation or tick transmission with B. burgdorferi-infected Ixodes scapularis larvae. Naïve larval ticks acquired both wild-type and mutant spirochetes with equal efficiency from B. burgdorferi-infected mice. The results demonstrate that BB0844 is not required for spirochete viability, pathogenicity, or maintenance in the tick vector or the mammalian host. At present, a defined role for BB0844 in B. burgdorferi cannot be ascertained.Borrelia burgdorferi, the Lyme disease pathogen, has a complex life cycle in nature which involves an arthropod vector and diverse mammalian hosts (6, 46). The type strain, B31, has a complex genome comprised of a linear chromosome and at least 21 linear and circular plasmids (12,19). The linear replicons have covalently closed hairpin telomeric ends (11, 24). The chromosome of B. burgdorferi strain B31 is 910,725 bp long and includes 853 putative open reading frames (ORFs) (19). A majority of the chromosomal sequence and gene order is conserved among B. burgdorferi strains; however, the chromosomes vary in length. These differences were shown to be the result of variability in the right telomeric region (10, 11) and have been confirmed by sequencing of additional B. burgdorferi genomes (40). It has been proposed that linear plasmid fragments were added to the right chromosomal telomere by means of nonhomologous recombination, after which portions of the transposed plasmid sequences underwent mutational decay (12,13,2...

Cyclic Di-GMP Receptor PlzA Controls Virulence Gene Expression through RpoS in Borrelia burgdorferi

“…3). As expected, the transcript level of ospC, as well as the transcript levels of several other RpoS-dependent genes, including bb0680, bb0844, bba07, and bba73, were greatly reduced in the plzA mutant in comparison to the wild-type and the complemented strains (7,45,53,54) (Fig. 3).…”

Borrelia burgdorferi bba66 Gene Inactivation Results in Attenuated Mouse Infection by Tick Transmission

“…Recent research investigating borrelia-vector interactions have focused on inactivation of global regulators, individual genes, and replicons to advance our understanding of B. burgdorferi tick colonization and persistence and vector transmission mechanisms (1,4,7,18,(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54). The loss of BBA66 activity did not completely abolish the ability of B. burgdorferi to invade the host by tick bite (at least when more than 4 ticks/mouse fed to repletion), but mouse infectivity was significantly impaired.…”

Use of in vivo Expression Technology for the Identification of Putative Host Adaptation Factors of the Lyme Disease Spirochete

“…The majority of the identified promoters have been described elsewhere, demonstrating the validity of the screen. Interestingly, all in vivo-induced promoters identified here have been shown to be a part of the mammalian-induced Rrp2-RpoN-RpoS regulon [Banik et al, 2011;Boardman et al, 2008;Caimano et al, 2004Caimano et al, , 2007Coleman and Pal, 2009;Ouyang et al, 2008;Yang et al, 2005]. This is consistent with the fact that products of RpoS-dependent genes such as ospC are not readily detected in our hands during standard in vitro culture [Casselli et al, 2012 and data not shown] but require shifting from 'tick-like' culture conditions (23 ° C) to 'mammalianlike' culture conditions (37 ° C) for maximal in vitro expression [Burtnick et al, 2007;Caimano et al, 2007].…”