Degnan Patrick H, Lazarus Adam B, Wernegreen Jennifer J
Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
Genome Res. 2005 Aug;15(8):1023-33. doi: 10.1101/gr.3771305.
The distinct lifestyle of obligately intracellular bacteria can alter fundamental forces that drive and constrain genome change. In this study, sequencing the 792-kb genome of Blochmannia pennsylvanicus, an obligate endosymbiont of Camponotus pennsylvanicus, enabled us to trace evolutionary changes that occurred in the context of a bacterial-ant association. Comparison to the genome of Blochmannia floridanus reveals differential loss of genes involved in cofactor biosynthesis, the composition and structure of the cell wall and membrane, gene regulation, and DNA replication. However, the two Blochmannia species show complete conservation in the order and strand orientation of shared genes. This finding of extreme stasis in genome architecture, also reported previously for the aphid endosymbiont Buchnera, suggests that genome stability characterizes long-term bacterial mutualists of insects and constrains their evolutionary potential. Genome-wide analyses of protein divergences reveal 10- to 50-fold faster amino acid substitution rates in Blochmannia compared to related bacteria. Despite these varying features of genome evolution, a striking correlation in the relative divergences of proteins indicates parallel functional constraints on gene functions across ecologically distinct bacterial groups. Furthermore, the increased rates of amino acid substitution and gene loss in Blochmannia have occurred in a lineage-specific fashion, which may reflect life history differences of their ant hosts.
专性细胞内细菌独特的生活方式能够改变驱动和限制基因组变化的基本力量。在本研究中，对宾夕法尼亚弓背蚁的专性内共生菌宾夕法尼亚布洛赫曼氏菌792 kb的基因组进行测序，使我们能够追踪在细菌 - 蚂蚁共生关系背景下发生的进化变化。与佛罗里达布洛赫曼氏菌的基因组比较发现，在辅因子生物合成、细胞壁和细胞膜的组成与结构、基因调控以及DNA复制等方面的基因存在差异丢失。然而，这两种布洛赫曼氏菌在共享基因的顺序和链方向上表现出完全保守。此前对蚜虫内共生菌布赫纳氏菌也有过类似基因组结构极度停滞的报道，这一发现表明基因组稳定性是昆虫长期细菌共生体的特征，并限制了它们的进化潜力。全基因组蛋白质差异分析显示，与相关细菌相比，布洛赫曼氏菌的氨基酸替代率快10至50倍。尽管基因组进化具有这些不同特征，但蛋白质相对差异之间存在显著相关性，表明在生态上不同的细菌群体中，基因功能受到平行的功能限制。此外，布洛赫曼氏菌中氨基酸替代率和基因丢失率的增加是以谱系特异性方式发生的，这可能反映了其蚂蚁宿主的生活史差异。
