Spirochaetes

Abstract

Species in the phylum Spirochaetes (order: Spirochaetales) are thin, spiral‐shaped or wave‐like, highly motile bacteria that are best visualised by darkfield microscopy. Spirochaetes are Gram‐negative‐like, in that they possess inner and outer membranes separated by a peptidoglycan‐containing periplasmic space. Beyond these ultrastructural similarities, few parallels exist with conventional Gram‐negative bacteria. There have been more than 90 spirochaete species identified, including the well‐known pathogenic, disease‐causing species Treponema pallidum (syphilis), Leptospira sp. (leptospirosis) and Borrelia burgdorferi (Lyme disease). The phylogenetic relationship among spirochaetes is evident at the level of gross phenotypic characteristics, which include a distinctive morphology derived from the presence of periplasmic flagella. In this article, the authors describe the genomic, physiologic, structural and functional features that make Spirochaetes unique among the prokaryotes. Key Concepts: Spirochaetes are a genetically and morphologically distinct group of bacteria. Spirochaetes are thin spiral‐shaped or wave‐like bacteria that are highly motile. Endoflagella/periplasmic flagella provide spirochaetes with their characteristic corkscrew‐like motility. Spirochaetes differ from typical Gram‐negative bacteria at the ultrastructural level. Spirochaetes are chemo‐organotrophic, grow in diverse conditions and are comprised of both pathogenic and nonpathogenic members. Complete genome sequencing has allowed for the characterisation and differentiation of spirochaetes at the genetic level. Medically important spirochaetes belong to the three genera Borrelia , Leptospira and Treponema .

The Remarkable Dual-Level Diversity of Prokaryotic Flagellins

“…4). However, the Spirochaetes contain very atypical flagella called "endoflagella" or "axial filaments," which are not exposed on the cell surface but located in the periplasmic space between the inner and outer membranes and drive a special form of motility (47,48), and the question arises as to how these are exposed to drive diversification. The Actinobacteria, the fourth largest bacterial phylum, form hyphae resembling fungal hyphae that grow by a combination of tip extension and branching of the hyphae; many have a mycelial lifestyle and propagate by forming spores (49).…”

Microbial life deep underground: From anaerobic cultures to reconstructed genomes

“…Spirochaetes are a highly motile group of bacteria with a characteristic spiral-like morphology. Representatives are chemoheterotrophic, thus obtaining their energy from the oxidation of organic compounds [33] and with a cell size than can be as small as 0.4 𝜇m in diameter [57]. Due to their unique morphology and small cell size, Spirochaetes have been described to pass 0.2 𝜇m membranes that are commonly used for sterile filtering [26].…”