据每日科学网日前报道,美国研究人员发现,线粒体与丰富的海洋细菌SAR11享有共同的进化祖先,这为研究线粒体这种十分重要的细胞器的起源提供了重要证据。
线粒体在形态、染色反应、化学组成、物理性质、活动状态、遗传体系等方面都很像细菌,所以人们推测,需氧细菌被原始真核细胞吞噬后,在长期互利共生中演化形成了现在的线粒体。不过这种内生学说缺乏有力证据。
夏威夷马诺大学及俄勒冈州立大学的研究人员利用多种相关的计算机程序,将线粒体及SAR11的基因组与多种真核生物的基因组进行了比对,并对基因组进行了非常复杂而又全面的系统进化分析,结果发现线粒体与海洋细菌SAR11有进化关系。
研究人员表示,这一发现激动人心,意义十分重大。夏威夷海洋与地球科学和技术学院海洋生物研究所的研究人员迈克尔认为,从生理学上讲,SAR11更容易依赖于其他生物,由于SAR11现在大量存在于海洋中,因此其祖先在古代海洋中可能也非常丰富,这就增加了其祖先与原始真核生物相接触的机会。
除了发现线粒体和SAR11之间的进化关系外,研究人员在以系统进化为基础评估基因组多样性的研究中还发现,丰富的海洋细菌SAR11具有遗传多样性。研究人员下一步将继续研究SAR11的新菌株及基因组,进一步了解其新陈代谢能力以及为什么它们会在海洋中如此成功地生存。 (生物谷Bioon.com)
doi:10.1038/srep00013
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Phylogenomic evidence for a common ancestor of mitochondria and the SAR11 clade
J. Cameron Thrash, Alex Boyd, Megan J. Huggett, Jana Grote, Paul Carini, Ryan J. Yoder, Barbara Robbertse, Joseph W. Spatafora, Michael S. Rappé & Stephen J. Giovannoni
Mitochondria share a common ancestor with the Alphaproteobacteria, but determining their precise origins is challenging due to inherent difficulties in phylogenetically reconstructing ancient evolutionary events. Nonetheless, phylogenetic accuracy improves with more refined tools and expanded taxon sampling. We investigated mitochondrial origins with the benefit of new, deeply branching genome sequences from the ancient and prolific SAR11 clade of Alphaproteobacteria and publicly available alphaproteobacterial and mitochondrial genome sequences. Using the automated phylogenomic pipeline Hal, we systematically studied the effect of taxon sampling and missing data to accommodate small mitochondrial genomes. The evidence supports a common origin of mitochondria and SAR11 as a sister group to the Rickettsiales. The simplest explanation of these data is that mitochondria evolved from a planktonic marine alphaproteobacterial lineage that participated in multiple inter-specific cell colonization events, in some cases yielding parasitic relationships, but in at least one case producing a symbiosis that characterizes modern eukaryotic life.