Spirochaetes
General information
Description and emendation
The phylum Spirochaetes represents a separate line of evolutionary descent in the bacterial domain. Three subgroups are clearly evident within the reference trees: Spirochaetaceae, 'Serpulinaceae', and Leptospiraceae, the last branching more deeply. A similar pattern is observed in PCA plots, in which the leptospiras form a discrete and well-separated cluster. The Spirochaetes remain remarkably uniform in morphology. All validly named species are Gram-negative, helically shaped, highly flexible cells. Motility by periplasmic flagella. Chemoorganotrophic. Anaerobic, microaerophilic, facultatively anaerobic, or aerobic. Free-living or associated with host animals (arthropods, mollusks, and mammals, including humans). Some species are pathogenic.