Table 1.

Effects of symbiosis on ciliate hosts and symbionts.

	Effects on host	Effects on symbiont
Positive	Supply of nutrients and organic matter, growth factors, vitamins etc. Competitive advantage Protection against parasites Oxygen removal by heterotrophs Degradation of metabolic waste; detoxification Protection against UV radiation Adaptation of aerobic life in anoxic zones	Nutrient supply movement to favorite conditions, increased motility grazing protection disposal of organic or inorganic material Less competitors Supply with CO2 and H2
Neutral or unclear	Space requirements by symbionts H2 scavengers in anaerobic ciliates (backup for methanogens?) Energy transfer? Higher grazing pressure?	Better genetic exchange? Constant conditions, e.g., pH?
negative	Competition for nutrients and organic matter cell lysis inhibition by toxins etc.	genetic bottleneck effect digestion by the host