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Cell's organelles give us evidence that they might have been independent organisms on their own.

Are there any single-cell microorganisms known to have gone so to say this way back as well, i.e. having some evidence to have their past as part of a larger organism?

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  • $\begingroup$ In the life-cycle of myxobacteria, there are uni- and multi-cellular stages. $\endgroup$
    – user37894
    Aug 17, 2018 at 17:40
  • $\begingroup$ It's not exactly what I've asked.. Slime molds same do not qualify. Still, good to know. $\endgroup$
    – J. Doe
    Aug 17, 2018 at 18:44
  • $\begingroup$ An organelle who did not come from an endosymbiosis does not contain DNA. It cannot just go away and leave on its own without hereditary material. A piece of DNA can however eventually leave a genome and become its own thing! $\endgroup$
    – Remi.b
    Sep 19, 2018 at 1:34

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Endosymbiosis leads to an irreversible loss of independence of the endosymbiont and the host.

For example, all members of the insect superfamily Aphidoidea (aphids) have an obligatory association with bacteria, commonly called primary endosymbionts (Munson et al., 1991; emphasis mine):

The primary endosymbionts are found in specialized organs, the mycetomes, which consist of cells (mycetocytes) containing the endosymbionts. The endosymbionts are enclosed within vesicles which are derived from the cell membranes of the mycetocytes.

None of the [primary] endosymbionts has been successfully cultivated in bacteriological media or in tissue culture. [These] organisms are essential for the life of the aphids since the removal of the endosymbionts by antibiotics leads to aphid sterility.

The endosymbionts are maternally transmitted, and there are complex mechanisms which assure that the progeny are infected.

Munson et al. (1991) Buchnera gen. nov. and Buchnera aphidicola sp. nov., a taxon consisting of the mycetocyte-associated, primary endosymbionts of aphids. Int J Syst Bacteriol 41: 566--568.

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    $\begingroup$ At SE we're looking for answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Otherwise how can the poster or anyone else know whether or not you are correct? See the Help for "how do I write a good answer?". $\endgroup$
    – David
    Aug 18, 2018 at 14:36

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