BIOL/CSES 4684

SPHAEROTILUS

SOIL MICROBIOLOGY

This webpage was created by Leslie Peverall

1. IDENTIFYING CHARACTERISTICS

Obligate aerobe
Filamentous bacteria.
Rod-shaped cells enclosed in a closely fitting sheath.
1.0-2.0 um wide and 3.0-8.0 um long.
Divides by binary fission.
Cells stain Gram negative.
Only one known species, S. natans.
False branching occurs, giving it a "tree branch"-like appearence.
Also known as a "sewage fungus".
Responsible for bulking in activated sludge.
Free cells are motile by flagella.
Neisser negative.
Has the ability to cause precipitation of iron oxides on it's sheaths.
Low dissolved oxygen(DO) concentrations.

The above picture shows S. natans under phase contrast microscopy (1000X).

2. TAXONOMIC DESCRIPTION
Sphaerotilus natans is a sheathed bacterium that constructs a tube-like sheath around each cell. The sheaths are composed of sugar and protein which protects the organisms from drying. The surface of the filamentous bacterium is covered with an acidic exopolysaccharide composed of glucose, fructose, galactose, and glucoronic acid. This composition makes the bacterium have a hydroscopic surface.

When the bacteria divides it doesn't separate, but clings to each other and forms a filament. The cells become free from the sheath when the nutrient supply is low. In order for the micro-organisms to grow there must be sufficient quantities of an available form of nitrogen and phosphorus, as well as other trace elements. False branching occurs from contiguous cytoplasm between trichomes sticking together and growning outward.

Morphological and physiological characteristics are similar to Leptothrix based on their 16s rRNA sequences. The are some differences between the two, Leptothrix isn't found in polluted areas and can oxidize magnesium, while the opposite is true for Sphaerotilus.
The above picture shows a free cell of S. natans under phase contrast microscopy (1000X).

3. ISOLATION AND ECOLOGY
Sphaerotilus is able to grow on fairly simple, soluble, readily metabolizable organic substrates. Stokes medium is also often used in the cultivation of S. natans. In this medium, glucose is present as the carbon source. One physiological characteristic used in the classification of S. natans is its ability to produce Poly-3-hydroxybutyrate(PHB). It accumulates more than 30% of PHB during the growth phase in pure culture. It can also convert amino acids into PHB when oxygen is limited.

Sphaerotilus is a typical inhabitant of activacted sludge. The water content of sludge floc increases as the bulk of the hydroscropic sheaths incease. Bulking is a problem at sewage treatment plants, which occurs when abundant sludge settles badly. This occurs when the water content of the sludge floc is greater when biomass is large. S. natans is strongly inhibited by sodium salts as well as by caprylate and caprate. Other control methods include, increasing the aeration basin DO concentration, increasing the mean cell residence time(MCRT), and by using aerobic, anoxic, or anaerobic selectors.

This picture shows Sphaerotilus natans in activated sludge bulking.

4. ADDITIONAL SOURCES OF INFORMATION
Gray, N. F. 1990. Activated Sludge. Oxford University Press. New York, NY. p.212

Jenkins, David, M.G. Richard, G.T. Daigger. 1999. Manual on the Causes and Control of Activated Sludge Bulking and Foaming. Second Edition. Lewis Publishers. Chelsea, Michigan. 46,118,80pp.

Madigan, Michael T., J.M. Martinko, J. Parker. 1997. Biology of Microorganisms. Eighth Edition. Prentice Hall. Upper Saddle River, NJ. 697 pp.

Takeda, Minoru, F. Nakano, T. Nagase, K. Iohara, J. Koizumi. 1998. Isolation and Chemical Composition of the Sheath of Sphaerotilus natans. Bioscience, Biotechnology, and Biochemistry, 62, 1138-1143.

5. LINKS TO OTHER SITES ON SPHAEROTILUS
Buckman Laboratories

Applied Microbiology and Biotechnology journal article

Database Central

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