Bacterial bedfellows:  a microscopic menage a trois may be responsible for a major step in evolution.
Sagan
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Margulis
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D000656:Amoeba / Q000166:cytology / Q000235:genetics; D000818:Animals; D001105:Archaea; D001419:Bacteria / Q000235:genetics; D005075:Biological Evolution; D004247:DNA; D005057:Eukaryotic Cells / Q000166:cytology / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D018087:Plastids / Q000502:physiology; D013144:Spirochaetales / Q000166:cytology; D013559:Symbiosis; D013822:Thermoplasma / Q000166:cytology
D004247:DNA