Abstract
Treponema pallidum subsp. endemicum (TEN) is the causative agent of endemic syphilis (bejel). Until now, only a single TEN strain, Bosnia A, has been completely sequenced. The only other laboratory TEN strain available, Iraq B, was isolated in Iraq in 1951 by researchers from the US Centers for Disease Control and Prevention. In this study, the complete genome of the Iraq B strain was amplified as overlapping PCR products and sequenced using the pooled segment genome sequencing method and Illumina sequencing. Total average genome sequencing coverage reached 3469×, with a total genome size of 1,137,653 bp. Compared to the genome sequence of Bosnia A, a set of 37 single nucleotide differences, 4 indels, 2 differences in the number of tandem repetitions, and 18 differences in the length of homopolymeric regions were found in the Iraq B genome. Moreover, the tprF and tprG genes that were previously found deleted in the genome of the TEN Bosnia A strain (spanning 2.3 kb in length) were present in a subpopulation of TEN Iraq B and Bosnia A microbes, and their sequence was highly similar to those found in T. p. subsp. pertenue strains, which cause the disease yaws. The genome sequence of TEN Iraq B revealed close genetic relatedness between both available bejel-causing laboratory strains (i.e., Iraq B and Bosnia A) and also genetic variability within the bejel treponemes comparable to that found within yaws- or syphilis-causing strains. In addition, genetic relatedness to TPE strains was demonstrated by the sequence of the tprF and tprG genes found in subpopulations of both TEN Iraq B and Bosnia A. The loss of the tprF and tprG genes in most TEN microbes suggest that TEN genomes have been evolving via the loss of genomic regions, a phenomenon previously found among the treponemes causing both syphilis and rabbit syphilis.
Highlights
The spirochete Treponema pallidum subsp. endemicum (TEN) causes endemic syphilis, a chronic infection usually localized to mucosal and skin lesions
Differences in the number of pseudogenes were found between the TEN Iraq B and Bosnia A genomes
A high-quality complete genome sequence for TEN Iraq B revealed close genetic relatedness between both available bejel-causing lab strains (i.e., Iraq B and Bosnia A) and genetic variability within the bejel treponemes comparable to that found within yaws- or syphilis-causing strains
Summary
The spirochete Treponema pallidum subsp. endemicum (TEN) causes endemic syphilis (bejel), a chronic infection usually localized to mucosal and skin lesions. Bejel and yaws are usually transmitted by direct skin-to-skin or skin-to-mucosa/mucosa-toskin contact with an infected person or by contact with contaminated utensils [4,6] and the contact is usually of a non-sexual nature, whereas syphilis is mainly venereally transmitted and can be transmitted from mother to child during pregnancy or during birth resulting in congenital syphilis. Recent studies by Noda et al [11] and Kawahata et al [12] have identified TEN in clinical samples from Cuban and Japanese patients, respectively, who had previously been diagnosed with syphilis
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