Dufresne Alexis, Salanoubat Marcel, Partensky Frédéric, Artiguenave François, Axmann Ilka M, Barbe Valérie, Duprat Simone, Galperin Michael Y, Koonin Eugene V, Le Gall Florence, Makarova Kira S, Ostrowski Martin, Oztas Sophie, Robert Catherine, Rogozin Igor B, Scanlan David J, Tandeau de Marsac Nicole, Weissenbach Jean, Wincker Patrick, Wolf Yuri I, Hess Wolfgang R
Station Biologique, Unité Mixte de Recherche 7127, Centre National de la Recherche Scientifique et Université Paris 6, BP74, 29682 Roscoff Cedex, France.
Proc Natl Acad Sci U S A. 2003 Aug 19;100(17):10020-5. doi: 10.1073/pnas.1733211100. Epub 2003 Aug 13.
Prochlorococcus marinus, the dominant photosynthetic organism in the ocean, is found in two main ecological forms: high-light-adapted genotypes in the upper part of the water column and low-light-adapted genotypes at the bottom of the illuminated layer. P. marinus SS120, the complete genome sequence reported here, is an extremely low-light-adapted form. The genome of P. marinus SS120 is composed of a single circular chromosome of 1,751,080 bp with an average G+C content of 36.4%. It contains 1,884 predicted protein-coding genes with an average size of 825 bp, a single rRNA operon, and 40 tRNA genes. Together with the 1.66-Mbp genome of P. marinus MED4, the genome of P. marinus SS120 is one of the two smallest genomes of a photosynthetic organism known to date. It lacks many genes that are involved in photosynthesis, DNA repair, solute uptake, intermediary metabolism, motility, phototaxis, and other functions that are conserved among other cyanobacteria. Systems of signal transduction and environmental stress response show a particularly drastic reduction in the number of components, even taking into account the small size of the SS120 genome. In contrast, housekeeping genes, which encode enzymes of amino acid, nucleotide, cofactor, and cell wall biosynthesis, are all present. Because of its remarkable compactness, the genome of P. marinus SS120 might approximate the minimal gene complement of a photosynthetic organism.
海洋中占主导地位的光合生物——海洋原绿球藻，主要有两种生态型：水柱上部适应强光的基因型和光照层底部适应弱光的基因型。本文报道的海洋原绿球藻SS120的全基因组序列，是一种极端适应弱光的类型。海洋原绿球藻SS120的基因组由一条1,751,080 bp的环状染色体组成，平均G+C含量为36.4%。它包含1,884个预测的蛋白质编码基因，平均大小为825 bp，一个rRNA操纵子和40个tRNA基因。与海洋原绿球藻MED4的1.66-Mbp基因组一起，海洋原绿球藻SS120的基因组是迄今为止已知的光合生物中最小的两个基因组之一。它缺少许多参与光合作用、DNA修复、溶质摄取、中间代谢、运动性、趋光性以及其他在其他蓝细菌中保守的功能的基因。即使考虑到SS120基因组的小尺寸，信号转导和环境应激反应系统的组成成分数量也显著减少。相比之下，编码氨基酸、核苷酸、辅因子和细胞壁生物合成酶的管家基因都存在。由于其显著的紧凑性，海洋原绿球藻SS120的基因组可能接近光合生物的最小基因互补。
