Sheathed Bacteria

Sheathed bacteria form chains of cells encased within a tube, or sheath (figure 11.22). This is thought to provide a protective function, helping the bacteria attach to solid objects located in favorable habitats while sheltering them from attack by predators. Masses of these filamentous sheaths can often be seen streaming from rocks or wood in flowing water polluted by nutrient-rich effluents. They often interfere with sewage treatment and other industrial processes by clogging pipes. Sheathed bacteria include species of Sphaerotilus and Leptothrix, which are Gram-negative rods.

Sheathed bacteria disperse themselves by forming swarmer cells, which have polar flagella and exit through the unattached end of the sheath. These motile cells move to a new solid surface, where they attach. If enough nutrients are present, they can multiply and form a new sheath, which elongates as the chain of cells grows.

Bilder Sphaerotilus

10 mm

Figure 11.22 Sheathed Bacteria Phase-contrast photomicrograph of a Sphaerotilus species.

10 mm

Figure 11.22 Sheathed Bacteria Phase-contrast photomicrograph of a Sphaerotilus species.

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