Shigenobu, S., Watanabe, H., Hattori, M., Sakaki, Y. & Ishikawa, H. (2000). Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS. Nature 407(6800): 81–86. doi:10.1038/35024074.
Key takeaways
From the reading, NOTE-1236.
- A small genome by loss. 640,681 bp, 583 ORFs, 26.3% G+C. The gene set is a subset of the ancestor shared with E. coli and H. influenzae, with no duplications of its own.
- Complementary and interlocked. Genes for the amino acids the aphid cannot make are kept; those for the ones it can are almost all gone, cysteine excepted. Host-made glutamate and aspartate are precursors of the symbiont’s products (THEORY-1103).
- Self-maintenance lost. No phospholipid synthesis except cls, almost no LPS genes, few transporters, no recA or uvrABC, and no transcriptional regulators except dnaA, though the genes they regulated are kept.
- Organelle-like, by inference. The authors propose that the host supplies phospholipid or the enzymes to make it, “like mitochondria do”. Nothing is tested.
- What it does not show. That the host cannot reproduce without Buchnera (cited, not shown), or how the genome shrank: drift is not mentioned.
Why this is here
A1 proposed a CASE for aphid–Buchnera, the obligate insect–bacterial association, and the record held Buchnera only through NOTE-114. This is the founding genome paper, registered as the primary source for CASE-173. The paper’s opening sentence says the mutualism “is so obligate that neither can reproduce independently”, citing earlier work. That is mutual dependence in the sense of LIT-1570, asserted here rather than shown: the genome shows the symbiont’s side only.