Ecology
Symbiont
An organism living in close physical association with another organism (the host) in a symbiotic relationship. May be mutualistic, parasitic, or commensal.
Biological Context
Mitochondria are ancient bacterial symbionts. Gut bacteria are symbionts essential for digestion. Coral zooxanthellae are photosynthetic symbionts. The degree of integration ranges from loose associations to essential partnerships where neither organism can survive alone.