Chapter 11 : Endosymbiotic Relationships

Abstract:

Symbiotic relationships between bacteria and eukaryotes (humans, animals, and plants) are generally beneficial to at least one of the partners involved. Facultative symbioses can arise, fade, and sometimes recur. Obligate symbioses, however, become established by evolution over time. They are particularly common in insects: 10 to 12% of insects carry intracellular symbionts, known as endosymbionts. Endosymbiosis has contributed to the evolutionary and ecological success of many insect species, providing properties that allow them to adapt to niches that would be otherwise inaccessible. The first endosymbionts are thought to have been mitochondria and chloroplasts in eukaryotic cells. In this process, a cell with a nucleus would have established an obligate symbiotic relationship with a photosynthetic bacterium, ultimately evolving into plant cell chloroplasts, or with a nonphotosynthetic bacterium, ultimately becoming the mitochondria found in all eukaryotic cells.