Archaea of the Miscellaneous Crenarchaeotic Group (MCG) exist widely in soil, freshwater and marine sediments of both surface and subsurface. However, current knowledge about this group is limited to its phylogenetic diversity. An archaeal 16S library was constructed from a sediment sample from the South China Sea, which was dominated by MCG and Marine Group I (MG-I). A metagenomic library was constructed from the same sediment sample, and three MCG fosmids (E6-3G, E37-7F and E48-1C) containing 16S rRNA genes were screened. Annotation showed that the three genomic fragments encode a variety of open reading frames (ORFs) that are potentially homologous to important functional genes related to lipid biosynthesis, energy metabolism, and resistance to oxidants. No colinear regions were found between MCG fosmids and reported archaeal genomic fragments or genomes, suggesting that the MCG archaea are quite different from the sequenced archaea in gene arrangement. Analyses of both the phylogenies of 16S rRNA genes and several informational processing genes and nucleotide frequencies showed that MCG archaea are distinct from MG-I plus relatives. In addition, tetranucleotide frequency analysis in combination with phylogenetic analysis suggested that some fragments in the MCG fosmids are probably derived from non-MCG or non-archaeal genomes.

中文翻译：

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杂类颅骨古生物群（MCG）的三个编码16S rRNA基因的fosmid片段的遗传结构：对海洋沉积古生菌的生理和进化的影响。

杂类颅骨类古细菌（MCG）广泛存在于表层和地下的土壤，淡水和海洋沉积物中。但是，有关该组的当前知识仅限于其系统发育多样性。利用来自南海的沉积物样本构建了一个古细菌16S库，该沉积物由MCG和第一海洋集团（MG-I）主导。从相同的沉积物样品构建宏基因组文库，并筛选了含有16S rRNA基因的三种MCG fosmids（E6-3G，E37-7F和E48-1C）。注释显示，这三个基因组片段编码各种开放阅读框（ORF），这些阅读框可能与与脂质生物合成，能量代谢和抗氧化剂相关的重要功能基因同源。在MCG fosmids和报告的古细菌基因组片段或基因组之间未发现共线区域，这表明MCG古细菌在基因排列上与测序古细菌完全不同。对16S rRNA基因和几个信息加工基因以及核苷酸频率的系统发育分析表明，MCG古细菌不同于MG-1及其亲戚。此外，四核苷酸频率分析与系统发育分析相结合表明，MCG fosmids中的某些片段可能源自非MCG或非古细菌基因组。对16S rRNA基因和几个信息加工基因以及核苷酸频率的系统发育分析表明，MCG古细菌不同于MG-1及其亲戚。此外，四核苷酸频率分析与系统发育分析相结合表明，MCG fosmids中的某些片段可能源自非MCG或非古细菌基因组。对16S rRNA基因和几个信息加工基因以及核苷酸频率的系统发育分析表明，MCG古细菌不同于MG-1及其亲戚。此外，四核苷酸频率分析与系统发育分析相结合表明，MCG fosmids中的某些片段可能源自非MCG或非古细菌基因组。