Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, San Juan de Alicante, 03550, Alicante, Spain.
Sci Rep. 2013;3:2471. doi: 10.1038/srep02471.
We describe a deep-branching lineage of marine Actinobacteria with very low GC content (33%) and the smallest free living cells described yet (cell volume ca. 0.013 μm(3)), even smaller than the cosmopolitan marine photoheterotroph, 'Candidatus Pelagibacter ubique'. These microbes are highly related to 16S rRNA sequences retrieved by PCR from the Pacific and Atlantic oceans 20 years ago. Metagenomic fosmids allowed a virtual genome reconstruction that also indicated very small genomes below 1 Mb. A new kind of rhodopsin was detected indicating a photoheterotrophic lifestyle. They are estimated to be ~4% of the total numbers of cells found at the site studied (the Mediterranean deep chlorophyll maximum) and similar numbers were estimated in all tropical and temperate photic zone metagenomes available. Their geographic distribution mirrors that of picocyanobacteria and there appears to be an association between these microbial groups. A new sub-class, 'Candidatus Actinomarinidae' is proposed to designate these microbes.
我们描述了海洋放线菌的一个深分枝谱系，其 GC 含量非常低（33%），并且拥有迄今发现的最小的自由生活细胞（细胞体积约为 0.013μm³），甚至比分布广泛的海洋光异养菌“海杆菌属 Pelagibacter ubique”还要小。这些微生物与 20 年前从太平洋和大西洋通过 PCR 获得的 16S rRNA 序列高度相关。宏基因组 fosmid 允许进行虚拟基因组重建，这也表明它们的基因组非常小，低于 1Mb。检测到一种新型视蛋白，表明它们具有光异养生活方式。据估计，它们在研究地点（地中海深叶绿素最大值）发现的总细胞数量中占~4%，在所有可用的热带和温带透光层宏基因组中也估计有相似数量的细胞。它们的地理分布与微微型蓝藻相似，这两个微生物群体之间似乎存在关联。提议建立一个新的亚目“海杆菌 Actinomarinidae”来指定这些微生物。
