Sheathed bacteria are filamentous microorganisms that produce a tubular extracellular sheath encasing a chain of cells. This flexible sheath provides protection and allows the filaments to attach to surfaces in flowing water environments.
Explanation
Members of genera such as Sphaerotilus, Leptothrix and Clonothrix are classic examples of sheathed bacteria. Their cells divide within a common sheath composed of polysaccharide and protein material secreted by the cells. As they grow, new cells elongate at the tip and the sheath extends, often becoming encrusted with iron or manganese oxides precipitated from the water. This encrustation gives rise to rusty or ochre deposits on stream beds and pipes. Leptothrix ochracea and related species oxidize dissolved iron, forming mineral-coated sheaths that contribute to iron cycling in freshwater ecosystems. Sphaerotilus natans forms long sheathed filaments that aggregate into slimy tassels in nutrient‑rich, slow‑flowing water and wastewater treatment plants; these growths, known as sludge bulking, can impede water flow and degrade water quality. Sheathed bacteria are not pathogenic to humans but are important for biofilm formation and metal deposition. Their sheaths protect against predation and provide a scaffold for the attachment of other microorganisms, creating complex biofilms in aquatic habitats.
Notable Features and Examples
- Leptothrix ochracea oxidizes ferrous iron to ferric hydroxide, producing brown, iron‑encrusted sheaths in springs and slow‑moving streams.
- Sphaerotilus natans forms colourless sheaths in polluted waters that can become iron‑encrusted in more pristine environments; excessive growth leads to sludge bulking in sewage treatment.
- Clonothrix fusca and other related genera produce sheaths encrusted with manganese oxide and thrive in water with high manganese concentrations.
- Sheathed bacteria contribute to biofilm communities and can cause fouling of water pipes and industrial equipment.
Though harmless to humans, sheathed bacteria play key roles in biogeochemical cycling of metals and can significantly impact water quality and infrastructure.
Related Terms: Filamentous Bacteria, Biofilm, Iron Bacteria, Sheath, Sphaerotilus