1. Organisms that live inside the cells of another organism in a mutually beneficial relationship; especially, bacteria or other microorganisms that have become integrated into eukaryotic cells.
Usage: biology; plural form of endosymbiont; commonly used in discussions of cell evolution and organelles

Examples

• Mitochondria are thought to have originated as endosymbionts billions of years ago.
• Chloroplasts in plant cells are believed to be endosymbionts that were incorporated through endosymbiosis.
• The theory of endosymbionts explains how eukaryotic cells acquired some of their organelles.
• Scientists study endosymbionts to understand the evolution of complex cells.
• Many endosymbionts have lost genes over time and become dependent on their host cells.
• The relationship between endosymbionts and their hosts demonstrates the power of symbiotic evolution.