Shigenobu S, Watanabe H, Hattori M, Sakaki Y, Ishikawa H
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan.
Nature. 2000 Sep 7;407(6800):81-6. doi: 10.1038/35024074.
Almost all aphid species (Homoptera, Insecta) have 60-80 huge cells called bacteriocytes, within which are round-shaped bacteria that are designated Buchnera. These bacteria are maternally transmitted to eggs and embryos through host generations, and the mutualism between the host and the bacteria is so obligate that neither can reproduce independently. Buchnera is a close relative of Escherichia coli, but it contains more than 100 genomic copies per cell, and its genome size is only a seventh of that of E. coli. Here we report the complete genome sequence of Buchnera sp. strain APS, which is composed of one 640,681-base-pair chromosome and two small plasmids. There are genes for the biosyntheses of amino acids essential for the hosts in the genome, but those for non-essential amino acids are missing, indicating complementarity and syntrophy between the host and the symbiont. In addition, Buchnera lacks genes for the biosynthesis of cell-surface components, including lipopolysaccharides and phospholipids, regulator genes and genes involved in defence of the cell. These results indicate that Buchnera is completely symbiotic and viable only in its limited niche, the bacteriocyte.
几乎所有蚜虫物种（同翅目，昆虫纲）都有60 - 80个巨大的细胞，称为含菌细胞，细胞内有圆形细菌，被命名为布赫纳氏菌。这些细菌通过宿主世代母系遗传给卵和胚胎，宿主与细菌之间的共生关系非常紧密，以至于两者都无法独立繁殖。布赫纳氏菌是大肠杆菌的近亲，但它每个细胞含有100多个基因组拷贝，其基因组大小仅为大肠杆菌的七分之一。在此，我们报告了布赫纳氏菌菌株APS的完整基因组序列，它由一条640,681碱基对的染色体和两个小质粒组成。基因组中有宿主必需氨基酸生物合成的基因，但非必需氨基酸的基因缺失，这表明宿主与共生体之间存在互补性和营养共生关系。此外，布赫纳氏菌缺乏包括脂多糖和磷脂在内的细胞表面成分生物合成基因、调节基因以及参与细胞防御的基因。这些结果表明，布赫纳氏菌完全是共生的，并且仅在其有限的生态位——含菌细胞中才能存活。
