Spirilla

Spirilla are bacteria characterized by a rigid, helical or spiral-shaped body. The term spirilla is used to describe organisms with a curved, corkscrew-like appearance, typically Gram-negative and motile. They differ from spirochetes in that spirilla generally have a more rigid cell wall and use external flagella for propulsion, whereas spirochetes are usually more flexible and use axial filaments for movement.

Morphology and motility of spirilla allow them to move in characteristic, rapid, twisting motions. Individual cells are usually a few micrometers long and can occur singly or in small groups. Most spirilla are aerobic or microaerophilic and rely on organic compounds for energy and carbon, though metabolic capabilities can vary among species.

Ecology and habitats of spirilla are diverse. They are commonly found in aquatic environments, including freshwater and marine systems, where they inhabit water columns, sediments, and biofilms. Some species may be associated with plants or organic matter in soils and sediments. They are generally free-living or part of the microbial communities in which they participate in nutrient cycles.

Taxonomy and examples: spirilla is a morphological term rather than a single taxonomic group, and multiple genera include spiral-shaped bacteria. Notable species historically associated with the term include Spirillum volutans, a large freshwater bacterium, and Spirillum serpens. Some species, such as Spirillum minus, have been linked to rat-bite fever in certain regions, illustrating that while many spirilla are environmental, others can be sinus pathogens or contributors to zoonotic disease.

In summary, spirilla are a morphologically defined group of spiral, typically Gram-negative and motile bacteria found in diverse aquatic and environmental niches, with varying degrees of clinical relevance.