Sphaerotilus

Sphaerotilus natans, in a river polluted with sewage

Sphaerotilus natans is a bacterium, which is nowadays the only one species of the genus Sphaerotilus. There are rod- shaped bacteria that form as a special thin-walled tubes in which they are arranged one behind the other. They occur in slow-flowing waters, ditches and ponds, which have a high content of biologically degradable substances. Because masses of these bacteria look through their arrangement in long tubes macroscopically like a mushroom spawn and occur in conjunction with wastewater, this bacterium is also called sewage fungus. However, communities of different thread- forming bacteria are referred to as sewage fungus in which S. natans is an essential part.

Properties

Straight, rod-shaped ( roughly cylindrical ) cells, diameter 1.2-2.5 microns, 1-10 microns length, gram- negative, at times each at one end of the cell subpolar a Flagellenbündel ( polytrich, monopolar flagella ). The bacteria swim freely ( " dreamer " ), but mostly they form longitudinal rows (single row chains of cells ), which are located in one of them deposited thin-walled tube of biological material. These tubes (similar Cases for edged weapons ) also referred to as sheaths, composed of biopolymers that form intertwined fibrils, and are smooth on the outside. They consist of 36-54 % carbohydrates, 12-28 % protein and 1-5 % lipids. The cells are not fixed to the tubes and can move in them. The sheath can be tacked to one end of solid surfaces. Outside of the vaginal mucus is deposited at times. At high concentrations of bioorganic substances in the medium can lead to growth and reproduction without sheaths. As a reserve substance polyhydroxybutyric is formed and deposited in the form of granules in the cells. The GC content of DNA is 68 to 71 mol%. Resting stages are not known.

Metabolism

The energy metabolism is strictly aerobic, oxidative, chemoorganoheterotroph. Be recycled a number of different bio-organic substances (among other polysaccharides, simple carbohydrates, some alcohols, amino acids, butyric acid and other organic acids). Glucose is metabolized by the citric acid cycle and Phosphogluconatweg. As nitrogen sources, amino acids, and ammonium and nitrate ions can be used. Vitamin B12 is needed. Even at low oxygen concentrations in the medium grows S. natans well.

Occurrence, ecology

S. natans is found in slow-flowing waters, ditches and ponds, which have a high content of bio-organic substances, especially in human sewage, agricultural waste water, waste water from factories in which paper or agricultural products (potatoes, milk, etc.) produced or processed be, and their cleaning equipment and in waters that are polluted with such effluents. The pH range of growth is from 5.4 to 9.0, the optimum pH is 6.5-7.6, the temperature range of the growth is 10-40 ° C, the optimum temperature is 20-30 ° C. salt- tolerance of the growth to 3-7 g / L sodium chloride (NaCl).

The envelope of the bacteria cells by sheaths has the advantage that in this way the filaments can be formed without the need for a cell extension or the formation of multicellular hyphae is required. Filaments cause a loose, high-surface- aggregation, which promotes the exchange of material with the surrounding medium. At the same time, the bacteria are protected from bacteriophages through the vaginal bacteria before eating creatures ( particularly protozoa ) and. The attachment to solid surfaces in flowing water provides the advantage that constantly new nutrients are introduced and metabolic products are washed away.

Technical significance

In wastewater treatment plants caused Sphaerotilus natans by the formation of masses of long, filamentous sheaths together with other fiber-forming bacteria (eg Haliscomenobacter ) the so-called bulking, a microorganism mass that floats in an aqueous medium with no or extremely slow sedimentation. The technically required separation of the microorganisms is prevented and disrupted the operation of the wastewater treatment plants. Also, it comes through the bulking sludge clogging of plants in the aquatic environment.

This damage below a sugar factory plays in the novel Pfister mill ( "Sewage novel" ) by Wilhelm Raabe a significant role. The bacterium is in this case not mentioned by name, but the typical shaggy masses of bacteria are described in the waters and a mill wheel. The story is a real case of water pollution by sewage basis of the sugar factory Rautheim in Braunschweig, where the botanist and microbiologist Ferdinand Cohn was involved as reviewers.