endosümbiont

An endosymbiont is an organism that lives inside another organism, the host. This relationship is known as endosymbiosis. The endosymbiont can benefit from the shelter and nutrients provided by the host, while the host may gain advantages such as enhanced metabolic capabilities or protection from other organisms.

A classic example of endosymbiosis is the relationship between certain bacteria and plant roots, where bacteria live within root cells and fix atmospheric nitrogen for the plant. Another prominent case is the origin of mitochondria and chloroplasts in eukaryotic cells. It is widely accepted that these organelles were once free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Over evolutionary time, these engulfed organisms became permanent endosymbionts, losing much of their independent genetic material and becoming integral parts of the host cell. This theory, known as the endosymbiotic theory, explains the presence of double membranes around mitochondria and chloroplasts and the existence of their own DNA, which resembles that of bacteria.

Endosymbiotic relationships can be obligate, meaning neither organism can survive without the other, or facultative, where the organisms can live independently but benefit from the association. The study of endosymbiosis provides crucial insights into evolutionary processes, particularly the development of cellular complexity and the diversification of life.