Abstract
The Spirochaetes species cause many important diseases including syphilis and Lyme disease. Except for their containing a distinctive endoflagella, no other molecular or biochemical characteristics are presently known that are specific for either all Spirochaetes or its different families. We report detailed comparative and phylogenomic analyses of protein sequences from Spirochaetes genomes to understand their evolutionary relationships and to identify molecular signatures for this group. These studies have identified 38 conserved signature indels (CSIs) that are specific for either all members of the phylum Spirochaetes or its different main clades. Of these CSIs, a 3 aa insert in the FlgC protein is uniquely shared by all sequenced Spirochaetes providing a molecular marker for this phylum. Seven, six, and five CSIs in different proteins are specific for members of the families Spirochaetaceae, Brachyspiraceae, and Leptospiraceae, respectively. Of the 19 other identified CSIs, 3 are uniquely shared by members of the genera Sphaerochaeta, Spirochaeta, and Treponema, whereas 16 others are specific for the genus Borrelia. A monophyletic grouping of the genera Sphaerochaeta, Spirochaeta, and Treponema distinct from the genus Borrelia is also strongly supported by phylogenetic trees based upon concatenated sequences of 22 conserved proteins. The molecular markers described here provide novel and more definitive means for identification and demarcation of different main groups of Spirochaetes. To accommodate the extensive genetic diversity of the Spirochaetes as revealed by different CSIs and phylogenetic analyses, it is proposed that the four families of this phylum should be elevated to the order level taxonomic ranks (viz. Spirochaetales, Brevinematales ord. nov., Brachyspiriales ord. nov., and Leptospiriales ord. nov.). It is further proposed that the genera Borrelia and Cristispira be transferred to a new family Borreliaceae fam. nov. within the order Spirochaetales.
Highlights
The phylum Spirochaetes consists of a large group of motile bacteria which are widespread in the environment and are highly prevalent disease causing agents (Seshadri et al, 2004; Paster, 2011a)
The phylum Spirochaetes is currently distinguished from other bacteria on the basis of both branching in 16S rRNA sequence based phylogenies and the presence of the endoflagella that characterizes the phylum (Paster, 2011a; Euzéby, 2013)
We have utilized comparative genomic techniques to identify large numbers of novel molecular signatures (CSIs) that are distinctive characteristics of either all members of the phylum Spirochaetes or for its different subgroups at multiple phylogenetic levels and which can be used to demarcate these groups in more definitive molecular terms
Summary
The phylum Spirochaetes consists of a large group of motile bacteria which are widespread in the environment and are highly prevalent disease causing agents (Seshadri et al, 2004; Paster, 2011a). Most spirochetes have one or more of these structures protruding from either pole of the cell, forming an axial filament, which gives rise to the characteristic jerky, corkscrewlike motility of the members of the phylum (Li et al, 2008; Paster, 2011a).Currently, the phylum Spirochaetes consists of 15 genera which are highly divergent in terms of their lifestyle and other characteristics (Euzéby, 2013) They live in marine sediments, deep within soil, commensally in the gut of arthropods, including termites, as well as in vertebrates as obligate parasites. Despite the diverse characteristics of its members, the phylum Spirochaetes is currently comprised of a single class, Spirochaetia, containing a single order, Spirochaetales, which is made up of four families (viz. Spirochaetaceae, Brachyspiraceae, Leptospiraceae, and Brevinemataceae) (Paster, 2011a; Euzéby, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
