nucleation

THEORY-1208: Bacterial endosymbionts lose their cell-envelope and envelope-transport genes together below about 400 kb and begin to lose translation genes below about 200 kb, and the host supplies the membranes, transport and protein synthesis that the smallest-genome symbionts no longer encode, as for organelles

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Properties5
StatusProposed
Tagsendosymbiosis, natural-sciences
SourceLIT-1571 — How do bacterial endosymbionts work with so few genes?
ExtendsTHEORY-1049 — On McCutcheon and colleagues' survey, bacterial endosymbionts lose their own cell-envelope and envelope-transport genes together below about 400 kb, and begin to lose translation genes (ribosomal proteins, tRNAs, aminoacyl-tRNA synthetases) below about 200 kb, so that the smallest-genome symbionts cannot be self-sufficient and their membranes, transport and protein synthesis are presumably supplied by the host, as for organelles
Bears onQUESTION-277 — When formerly autonomous partners come to depend on one another, which of mutual dependence, reproductive cohesion, the distribution of essential functions across genomes, the host's regulatory control and the alignment of selection does each route to dependence bring about, and which of them, alone or together, make the partnership a new evolutionary individual?

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Source

McCutcheon, Garber, Spencer & Warren (2024), LIT-1571, read in full in NOTE-1213. The paper’s conclusion is that such symbionts can only work if the host supplies what they no longer encode, and it leaves how as four open mysteries.

Where the evidence stands

What the paper shows, and what it does not, is THEORY-1049, Active, which this entry extends: that entry is the reading, this one the thesis. The promote_when above is THEORY-1049’s condition before the twenty-second status review promoted it, carried here unchanged, because it asks what would make the thesis true and not what the paper says.

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