Beggiatoa is a filamentous bacterium possessing the following characteristics:
- not branched; - mobile (gliding movement);
- straight/ bowed filaments, free in the water between the flocs;
- variable filament length;
- cell diameter 1.5 to 2.5 µm;
- no attached growth;
- no sheath;
- septa sometimes visible;
- rectangular cells;
- in vivo sulphur storage;
- Gram negative;
- Neisser negative.

The combination of sulphur granules in the filaments with the gliding movement is so characteristic of Beggiatoa sp. that they cannot be confused with other species.

Occurrence in activated sludge

Beggiatoa occurs in treatment plants where a lot of reduced sulphur compounds are present in the influent (H2S !) and/or a major lack of oxygen. The filaments do not actually affect the settling velocity of the flocs. Beggiatoa is far more an indicator organism

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