Amoebae

Shape changing naked amoebae and shelled (testate) amoebae.

Sketch: amoebae as typically seen at 100x to 400x. Not to scale.

Under the microscope

Large naked amoeba next to bacterial floc and a bacterial filament, labeled, phase contrast at 400x — **Naked amoeba.** Large naked amoeba beside a bacterial floc and filament. Phase contrast, 400x. **What this indicates:** Naked amoebae in numbers suggest a young sludge, a startup or recovery after an upset. One or two on a slide is normal.

Photomicrographs from Brad Musick's microscope slide collection.

Illustrated

Naked and testate amoebae. A naked amoeba with pseudopods and vacuoles, and two shelled (testate) amoebae, Arcella and Euglypha. What this indicates: Many naked amoebae suggest a young sludge or a recovery from upset; testate amoebae suggest a long SRT, low F/M and often full nitrification. Original illustration for this site, not to scale.

See all microscopy illustrations

What you see

Naked amoebae: shapeless cells that move by flowing cytoplasm (pseudopods). Slow moving, often easy to miss.
Testate amoebae (Arcella, Euglypha): amoebae in a round or vase shaped shell, often brown, with pseudopods extending from an opening.

What it may indicate

Naked amoebae in large numbers: young sludge, startup, recovery after an upset, high F/M or low DO.
Testate amoebae: typically long SRT, low F/M, stable nitrifying sludge, sometimes extended aeration.

What process data to check next

SRT and F/M: are you running very young or very old sludge?
DO profile.
Recent upset or washout.
Ammonia: testate amoebae often coincide with full nitrification.

One slide is a snapshot. Look at trends over several days and compare with SRT, F/M, DO, SVI and effluent quality before you change anything.