Source
Shigenobu, Watanabe, Hattori, Sakaki & Ishikawa (2000), Nature 407: 81–86, LIT-1596, read in full in NOTE-1236 from the publisher’s free PDF. The whole letter, Table 1, the captions of Figures 1–3, and the Methods.
What was actually shown
- The sequence. One chromosome of 640,681 bp with 583 ORFs, and two plasmids carrying leucine and tryptophan genes. 500 ORFs have an assigned function and only 4 are unique to Buchnera. Gene order in E. coli operons is conserved.
- Amino acids (Fig. 2). Genes for the amino acids essential to aphids are present, with a few gaps (ilvE, dapC). Genes for the non-essential ones “are almost completely missing”, cysteine excepted. Glutamate and aspartate, which Buchnera cannot make, are precursors of essential amino acids.
- What else is missing. Phospholipid synthesis except cls; LPS synthesis except lpcA and kdtB; every transcriptional regulator except dnaA; recA, uvrABC, lexA, umuCD; restriction and methylation genes. The genes the lost regulators once controlled are kept.
- Loss, not a small ancestor. The gene set is “a small subset” of the inferred ancestor shared with E. coli and H. influenzae, with no lineage-specific duplications.
What could have failed: Buchnera could have kept a broad, E. coli-like biosynthetic repertoire, or lost the essential-amino-acid pathways as parasites lose theirs. The gene set could have been a small ancestor’s, with duplications of its own. None of these is what the sequence shows.
What this does not say
- Not that neither partner can reproduce alone. That is the paper’s opening sentence, cited to earlier work. The genome speaks to the symbiont’s side only.
- Not that the host supplies membrane lipids. The authors offer two routes, import of host phospholipid or host enzymes “like mitochondria do”, and test neither.
- Not that the host controls the symbiont’s genes. The symbiont has lost its own regulators. Nothing here shows the host regulating it.
- Not how the genome shrank. The paper names no population-genetic mechanism. Drift and Muller’s ratchet are LIT-1573’s account, not this paper’s.
- Not gene transfer to the host. The host genome is not studied, so transfer in either direction is neither found nor excluded.
Connections
- QUESTION-277. The clearest worked instance in the record of the distribution of essential functions (G) between two genomes, interlocked by shared precursors. It shows the symbiont’s dependence (D) from gene content and asserts the host’s. It shows loss of the symbiont’s self-regulation, which is not yet host control (C).
- THEORY-1049. At 641 kb, Buchnera APS has already lost phospholipid synthesis and almost all of LPS synthesis, while keeping fatty-acid, murein and sec genes. So envelope erosion begins above the 400 kb threshold, which then marks complete loss. The comparison is mine.
- CASE-173 is the case this account documents.
Note of 2026-10-30: promoted, and the wider thesis filed beside it
The twenty-second status review promoted this reading under ADR-065: it reports what Shigenobu and colleagues’ genome shows and what they infer from it, and NOTE-1236 read the paper in full. Whether Buchnera’s metabolism interlocks with its host’s as inferred is THEORY-1219’s question, Proposed, which keeps this entry’s old promote_when.