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An endosymbiont or endobiont [1] is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia ), which live in the root nodules of legumes , single-cell algae inside reef-building corals , and bacterial endosymbionts ...
The original theory by Lynn Margulis proposed an additional preliminary merger, but this is poorly supported and not now generally believed. [1] Symbiogenesis (endosymbiotic theory, or serial endosymbiotic theory [2]) is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. [3]
The theory of endosymbiosis, as known as symbiogenesis, provides an explanation for the evolution of eukaryotic organisms. According to the theory of endosymbiosis for the origin of eukaryotic cells, scientists believe that eukaryotes originated from the relationship between two or more prokaryotic cells approximately 2.7 billion years ago.
A symbiosome is formed as a result of a complex and coordinated interaction between the symbiont host and the endosymbiont. [5] At the point of entry into a symbiont host cell, part of the cell's membrane envelops the endosymbiont and breaks off into the cytoplasm as a discrete unit, an organelle-like vacuole called the symbiosome.
I greatly admire Lynn Margulis's sheer courage and stamina in sticking by the endosymbiosis theory, and carrying it through from being an unorthodoxy to an orthodoxy. I'm referring to the theory that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells.
The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryotic host in the archaea, giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen (symbiogenesis).
As the endosymbiont adapts to the host's lifestyle, the endosymbiont changes dramatically. There is a drastic reduction in its genome size, as many genes are lost during the process of metabolism , and DNA repair and recombination, while important genes participating in the DNA-to-RNA transcription , protein translation and DNA/RNA replication ...
One theory is that the microorganisms circulating in the hemolymph of the mother migrate to a posterior region of the offspring blastula containing enlarged follicle cells. Other studies suggest that symbionts are directly transferred from the maternal bacteriocyte to the follicular region of the blastula through exocytic and endocytic transport.