Abstract
DNA methyltransferases have been implicated in the regulation of virulence genes in a number of pathogens. Relapsing fever Borrelia species harbor a conserved, putative DNA methyltransferase gene on their chromosome, while no such ortholog can be found in the annotated genome of the Lyme disease agent, Borrelia burgdorferi. In the relapsing fever species Borrelia hermsii, the locus bh0463A encodes this putative DNA adenine methyltransferase (dam). To verify the function of the BH0463A protein product as a Dam, the gene was cloned into a Dam-deficient strain of Escherichia coli. Restriction fragment analysis subsequently demonstrated that complementation of this E. coli mutant with bh0463A restored adenine methylation, verifying bh0463A as a Dam. The requirement of bh0463A for B. hermsii viability, infectivity, and persistence was then investigated by genetically disrupting the gene. The dam- mutant was capable of infecting immunocompetent mice, and the mean level of spirochetemia in immunocompetent mice was not significantly different from wild type B. hermsii. Collectively, the data indicate that dam is dispensable for B. hermsii viability, infectivity, and persistence.
Highlights
Relapsing fever is an arthropod-borne disease caused by several species of spirochetal bacteria in the genus Borrelia
Plasmid DNA extracted from the dam- E. coli transformed clones was subjected to digestion with either DpnI, MboI, or Sau3AI; DpnI cuts GATC sites in which the adenine residue is methylated, MboI cuts unmethylated GATC sites, and Sau3AI cleaves all GATC sites regardless of adenine methylation, but will not cut when cytosine is methylated
It has been previously reported that adenine methylation systems are found in relapsing fever Borrelia spp., but are absent in most B. burgdorferi strains [22, 23]
Summary
Relapsing fever is an arthropod-borne disease caused by several species of spirochetal bacteria in the genus Borrelia. Several species of relapsing fever are found in North America and cause sporadic illness, including the well-characterized species Borrelia hermsii [3]. The pathogenesis of relapsing fever Borrelia spp. is distinct from that of the closely related agent of Lyme. Relapsing fever Borrelia spp. cause acute recurrent febrile events that correspond to episodic high levels of bacteremia, whereas B. burgdorferi rapidly migrate out of the bloodstream and into host tissues that results in various clinical syndromes including arthritis, neuropathy, and carditis [6, 7]. B. burgdorferi and relapsing fever Borrelia spp. share many orthologous genes and exhibit significant synteny on their chromosomes [8, 9]. The bh0463A gene of B. hermsii codes for a putative DNA adenine methyltransferase (Dam), and is one example of a gene found only in relapsing fever-type spirochetes [9]
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