Sewage fungus
Sphaerotilus
Sphaerotilus is a genus of filamentous bacteria belonging to the order Burkholderiales. The cells are rod-shaped and grow in long chains within a protective organic sheath. In nutrient-rich flowing waters, the species Sphaerotilus natans often forms massive, cotton-like colonies known as sewage fungus. They are a classic indicator of heavy pollution with easily biodegradable organic substances.
Details
Identification
Filamentous growth, formation of sheaths, rod-shaped individual cells (1-2 x 3-10 µm), formation of swarmer cells with polar flagella.
Social behavior
Formation of filamentous colonies (biofilms) by attachment to substrates using holdfasts.
Diet
Utilizes dissolved organic substances such as sugars, alcohols, amino acids, and organic acids (chemoorganotrophic).
Ecology
Ecological role
Important role in decomposing organic loads in running waters; can cause oxygen depletion during mass developments.
Natural predators
Protozoa (ciliates), rotifers, and small oligochaetes.
Competitor species
Other filamentous bacteria like Beggiatoa or fungi at lower pH levels.
Ecosystem service
Self-purification of water bodies by decomposing carbohydrates and nitrogen compounds.
Threats
Improvement of wastewater treatment (nutrient removal), extreme pH levels.
Scientific profile
Profile
Habitat
Typically found in lotic waters with heavy organic pollution, particularly from food industry effluents (sugar refineries, dairies) or paper mills. It inhabits the polysaprobic to alpha-mesosaprobic zones and requires a continuous supply of dissolved nutrients alongside the presence of dissolved oxygen.
Ecological role
Sphaerotilus plays a central role in the decomposition of dissolved organic matter in polluted waters. However, during mass developments, it can smother macrozoobenthos, damage fish eggs, and lead to fish kills due to nocturnal oxygen depletion.