Sanchez Sophie, Hourdez Stéphane, Lallier François H
Laboratoire Adaptation et Diversité en Milieu Marin, UPMC CNRS UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, 29682 Roscoff cedex.
J Soc Biol. 2007;201(3):247-57. doi: 10.1051/jbio:2007036.
Oxygen appears to be one of the key factors in understanding the evolution of life on Earth. Almost absent during more than 2 billion years, its subsequent increase is correlated with the emergence of oxygenic photosynthesis by Cyanobacteria, followed by aerobic Prokaryotes and eventually Eukaryotes, all primitively aerobic, and more recently, the development of complex multicellular organisms. However, in some reduced environments, still present at the surface of the Earth and even more so in ocean depths (hydrothermal vents, cold seeps, massive organic falls,...), anaerobic or micro-aerobic Prokaryotes continue to grow, including some chemoautotrophic bacteria deriving energy from sulfide oxidation for instance. A few Metazoa have managed to collaborate with such chemoautotroph Prokaryotes, the most abundant species forming endosymbiotic associations. The most studied of these endosymbioses (the mussels Bathymodiolus, the vestimentiferan tubeworm Riftia pachyptila, or the clams Calyptogena) have revealed important differences in the degree of interdependence between host and symbionts, and in the mode of symbiont transmission. The evolutive process of these symbioses is reminiscent of the primary endosymbioses which have given rise to the organelles of heterotrophic Eukaryotes (mitochondria) and phototrophic Eukaryotes (chloroplasts). The study of these modern days biological models could shed light on symbiogenesis itself and also potentially reveal thiotrophic Eukaryotes as a new lineage.
氧气似乎是理解地球生命演化的关键因素之一。在超过20亿年的时间里几乎不存在，其随后的增加与蓝细菌进行的产氧光合作用的出现相关，随后是需氧原核生物，最终是真核生物，所有这些最初都是需氧的，以及最近复杂多细胞生物的发展。然而，在一些还原环境中，仍然存在于地球表面，在海洋深处（热液喷口、冷泉、大量有机沉降物等）更是如此，厌氧或微需氧原核生物继续生长，包括一些例如从硫化物氧化中获取能量的化学自养细菌。一些后生动物已经设法与这种化学自养原核生物合作，最丰富的物种形成内共生关系。对这些内共生关系研究最多的（贻贝属的 Bathymodiolus、巨型管虫属的 Riftia pachyptila 或蛤属的 Calyptogena）揭示了宿主与共生体之间相互依赖程度以及共生体传播方式的重要差异。这些共生关系的进化过程让人联想到导致异养真核生物（线粒体）和光合真核生物（叶绿体）细胞器产生的原始内共生关系。对这些现代生物学模型的研究可以阐明共生起源本身，也有可能揭示硫营养真核生物作为一个新的谱系。
