General Medicine

It is generally accepted that diverse, poorly characterized microorganisms reside deep within Earth’s crust. One such lineage of deep subsurface-dwelling bacteria is an uncultivated member of the Firmicutes phylum that can dominate molecular surveys from both marine and continental rock fracture fluids, sometimes forming the sole member of a single-species microbiome. Here, we reconstructed a genome from basalt-hosted fluids of the deep subseafloor along the eastern Juan de Fuca Ridge flank and used a phylogenomic analysis to show that, despite vast differences in geographic origin and habitat, it forms a monophyletic clade with the terrestrial deep subsurface genome of “Candidatus Desulforudis audaxviator” MP104C. While a limited number of differences were observed between the marine genome of “Candidatus Desulfopertinax cowenii” modA32 and its terrestrial relative that may be of potential adaptive importance, here it is revealed that the two are remarkably similar thermophiles possessing the genetic capacity for motility, sporulation, hydrogenotrophy, chemoorganotrophy, dissimilatory sulfate reduction, and the ability to fix inorganic carbon via the Wood-Ljungdahl pathway for chemoautotrophic growth. Our results provide insights into the genetic repertoire within marine and terrestrial members of a bacterial lineage that is widespread in the global deep subsurface biosphere, and provides a natural means to investigate adaptations specific to these two environments.

Recently, a novel species of the genusBorreliawas identified inBothriocroton concolorandIxodes holocyclusticks from echidnas. Analyses of 16S rRNA andflaBgenes identified three closely related genotypes of this bacterium (Borreliasp. Aus A-C) that were unique and distinct from previously described borreliae. Phylogenetic analyses offlaB(763 bp),groEL(1537 bp),gyrB(1702 bp) andglpQ(874 bp) gene sequences and concatenated sequences (3585 bp) of three gene loci (16S rRNA,flaBandgyrB) were consistent with previous findings and confirm that this novel species of the genusBorreliais more closely related to, yet distinct from, the Reptile-associated (REP) and Relapsing Fever (RF) groups. At theflaBlocus, genotypes A, B and C shared the highest percentage sequence similarities (87.9, 88 and 87.9 %, respectively) withB.orrelia turcica(REP), whereas at thegroELandgyrBloci, these genotypes were most similar (88.2–89.4 %) toB.orrelia hermsii(RF). At theglpQlocus, genotypes A and B were most similar (85.7 and 85.4 % respectively) toBorreliasp. Tortoise14H1 (REP). The presence of theglpQgene, which is absent in the Lyme Borreliosis group spirochaetes, further emphasises that the novel species of the genusBorreliacharacterized in the present study does not belong to this group. Phylogenetic analyses at multiple loci produced consistent topographies revealing the monophyletic grouping of this bacterium, therefore providing strong support for its species status. We propose the name ‘CandidatusBorreliatachyglossi’, and hypothesize that this species of the genusBorreliamay be endemic to Australia. The pathogenic potential of this bacterium is not yet known.