Kidney ciliate
Colpidium colpoda
Colpidium colpoda is a single-celled ciliate characterized by its distinct kidney-like shape. It reaches a length of approximately 50 to 150 micrometers and is entirely covered in cilia for locomotion. This species is a well-known indicator for highly organically polluted waters (polysaprobic zones). It feeds primarily on bacteria, which it ingests through a specialized oral groove, playing a key role in the microbial loop.
Details
Identification
Kidney-shaped body, uniform ciliation, contractile vacuole in the posterior third, large macronucleus, size 50-150 µm.
Social behavior
Solitary, but forms extremely dense populations when food supplies (bacterial blooms) are abundant.
Diet
Pure bacterivore that filters bacteria from the surrounding water.
Hunting strategy
Creation of a water current through ciliary movement to direct bacteria into the peristome.
Overwintering
Formation of resting stages (cysts) under unfavorable environmental conditions.
Ecology
Ecological role
Primary consumer in the microbial loop; converts bacterial biomass into energy available for higher organisms.
Natural predators
Larger predatory ciliates (e.g., Didinium), rotifers, and small planktonic crustaceans.
Competitor species
Other bacterivorous ciliates such as Paramecium or Glaucoma.
Ecosystem service
Contributes to the biological self-purification of water bodies and wastewater treatment in sewage plants.
Threats
No acute threat; sensitive to toxic chemicals that destroy bacterial life.
Scientific profile
Profile
Habitat
Freshwater ecosystems, especially stagnant or slow-flowing waters with high organic load. Frequently found in activated sludge of wastewater treatment plants and polysaprobic waters.
Reproduction
Asexual reproduction by transverse binary fission. Conjugation (sexual process for genetic exchange) may occur under stress conditions.
Ecological role
Important primary consumer in the microbial loop; regulates bacterial populations and serves as a link to higher trophic levels.