Department of Biology, University of Utah, Salt Lake City, Utah, United States of America.
PLoS Genet. 2012;8(11):e1002990. doi: 10.1371/journal.pgen.1002990. Epub 2012 Nov 15.
Despite extensive study, little is known about the origins of the mutualistic bacterial endosymbionts that inhabit approximately 10% of the world's insects. In this study, we characterized a novel opportunistic human pathogen, designated "strain HS," and found that it is a close relative of the insect endosymbiont Sodalis glossinidius. Our results indicate that ancestral relatives of strain HS have served as progenitors for the independent descent of Sodalis-allied endosymbionts found in several insect hosts. Comparative analyses indicate that the gene inventories of the insect endosymbionts were independently derived from a common ancestral template through a combination of irreversible degenerative changes. Our results provide compelling support for the notion that mutualists evolve from pathogenic progenitors. They also elucidate the role of degenerative evolutionary processes in shaping the gene inventories of symbiotic bacteria at a very early stage in these mutualistic associations.
尽管进行了广泛的研究，但对于栖息在世界上约 10%昆虫体内的互利共生细菌内共生体的起源仍知之甚少。在这项研究中，我们对一种新型机会性病原体“菌株 HS”进行了特征描述，发现它与昆虫内共生体 Sodalis glossinidius 密切相关。我们的研究结果表明，菌株 HS 的祖先曾作为独立进化的 Sodalis 相关内共生体的祖先，而这些内共生体存在于多种昆虫宿主中。比较分析表明，昆虫内共生体的基因库是通过不可逆的退化变化组合，从一个共同的祖先模板中独立衍生而来的。我们的研究结果为共生体从病原祖先进化而来的观点提供了有力的支持。它们还阐明了在这些互利共生关系的早期阶段，退化进化过程在塑造共生细菌的基因库方面所起的作用。
