Taxonomy
- Domain: Bacteria
- Phylum: Proteobacteria
- Class: Betaproteobacteria
- Order: Nitrosomonadales
- Family: Spirillaceae
- Genus: Spirillum
- Species: Spirillum volutans
Morphology
Spirillum volutans is a large, helical, gram‑negative bacterium, typically measuring 30–60 µm in length and 1–2 µm in width. The cells possess a rigid, spiral‑shaped body with a pronounced curvature, giving them a “coiled” appearance. Motility is conferred by a single polar flagellum, which can rotate rapidly, enabling the organism to swim in aqueous environments.
Physiology
The species is an obligate aerobe, requiring dissolved oxygen for growth. It metabolizes a variety of organic substrates, primarily utilizing them in oxidative pathways. The organism is chemoorganotrophic and does not fix nitrogen. Growth is optimal at neutral to slightly alkaline pH and moderate temperatures (20–30 °C).
Ecology and Habitat
Spirillum volutans is commonly isolated from freshwater habitats, including ponds, lakes, and slow‑moving streams. It is frequently associated with sediments and the surface microlayer of water bodies, where oxygen concentrations are sufficient. The bacterium is not known to be pathogenic to humans, animals, or plants.
Historical Background
The species was first described by the German microscopist Christian Gottfried Ehrenberg in 1830, based on observations of its distinctive coiled morphology in water samples. It subsequently became the type species for the genus Spirillum.
Research Significance
Due to its considerable size and pronounced spiral shape, S. volutans has been employed as a model organism for studying bacterial motility, flagellar architecture, and cell‐shape determination. Its large dimensions also facilitate microscopic examination of intracellular structures without the need for advanced imaging techniques.
Genomic Information
Whole‑genome sequencing of S. volutans strains has been completed, revealing a genome size of approximately 3.5 Mbp with a G+C content of ~55 mol %. Genomic analyses indicate the presence of genes encoding multiple oxidases, transport systems for organic acids, and flagellar assembly proteins.
Clinical Relevance
There are no documented cases of Spirillum volutans causing disease in humans or animals. Consequently, it is considered non‑pathogenic and is generally regarded as an environmental bacterium of limited clinical importance.
