Convergent evolution of metabolic roles in bacterial co-symbionts of insects
Convergent evolution of metabolic roles in bacterial co-symbionts of insects
复制标题
DOI：
10.1073/pnas.0906424106
复制
发表时间：
2009-09-08
影响因子：
11.1
通讯作者：
Moran, Nancy A.
中科院分区：
文献类型：
--
作者：
McCutcheon, John P.;McDonald, Bradon R.;Moran, Nancy A.
严格依赖宿主的生活方式对细菌基因组有着深远的进化影响。最突出的是有时戏剧性的数量的基因丢失和基因组减少。最近，来自神枪手的共存细胞内共生体的高度减少的基因组显示出惊人的代谢相互依赖性。其中一种共生体，称为Sulcia muelleri（拟杆菌），可以产生10种必需氨基酸中的8种，尽管它的基因组只有245 kb。另一种是Baumannia cicadellinicola（γ-变形菌门），可以产生剩下的两种必需氨基酸以及许多维生素。蝉也含有共生体Sulcia，但缺乏Baumannia，而是含有共生共生体Hodgkinia cicadicola（α-变形菌门）。在这里，我们报告说，尽管存在至少2亿年的分歧，但两个沟基因组具有几乎相同的基因内容和基因顺序。此外，我们表明，尽管是遗传学上的遥远和基因组的大小和结构有很大的不同，霍奇金氏和Baumannia已经收敛在基因集赋予相似的能力，必需氨基酸的生物合成，在这两种情况下，精确互补的途径，在Sulcia保守。相反，它们具有完全不同的维生素生物合成能力。尽管霍奇金氏菌具有细菌中已知的最小基因组，但其蛋白质组的至少7%用于钴胺素（维生素B-12）的生物合成，这是一个重要的代谢负担。这些基因的存在可以通过霍奇金氏保留钴胺素依赖型的甲硫氨酸合酶而不是在鲍曼不动杆菌中发现的钴胺素非依赖型来解释，这种情况需要保留钴胺素生物合成能力来制造必需氨基酸甲硫氨酸。
A strictly host-dependent lifestyle has profound evolutionary consequences for bacterial genomes. Most prominent is a sometimes-dramatic amount of gene loss and genome reduction. Recently, highly reduced genomes from the co-resident intracellular symbionts of sharpshooters were shown to exhibit a striking level of metabolic interdependence. One symbiont, called Sulcia muelleri (Bacteroidetes), can produce eight of the 10 essential amino acids, despite having a genome of only 245 kb. The other, Baumannia cicadellinicola (gamma-Proteobacteria), can produce the remaining two essential amino acids as well as many vitamins. Cicadas also contain the symbiont Sulcia, but lack Baumannia and instead contain the co-resident symbiont Hodgkinia cicadicola (alpha-Proteobacteria). Here we report that, despite at least 200 million years of divergence, the two Sulcia genomes have nearly identical gene content and gene order. Additionally, we show that despite being phylogenetically distant and drastically different in genome size and architecture, Hodgkinia and Baumannia have converged on gene sets conferring similar capabilities for essential amino acid biosynthesis, in both cases precisely complementary to the pathways conserved in Sulcia. In contrast, they have completely divergent capabilities for vitamin biosynthesis. Despite having the smallest gene set known in bacteria, Hodgkinia devotes at least 7% of its proteome to cobalamin (vitamin B-12) biosynthesis, a significant metabolic burden. The presence of these genes can be explained by Hodgkinia's retention of the cobalamin-dependent version of methionine synthase instead of the cobalamin-independent version found in Baumannia, a situation that necessitates retention of cobalamin biosynthetic capabilities to make the essential amino acid methionine.