从宏基因组推测扎龙湿地未培养甲烷古菌Rice Cluster II的代谢途径与可能的盐碱适应性

Metagenomic analysis of metabolic pathways and possible saline-alkaline adaptation of uncultured methanogens of Rice Cluster Ⅱ in Zhalong wetland

摘要:

【背景】湿地是重要的甲烷排放源，因为其中栖息着各种产甲烷古菌。已知未培养甲烷古菌Rice Cluster II (RCII)类群广泛分布于低温酸性和北方泥炭藓湿地、淡水湿地及草本沼泽等环境，但它们在低温盐碱湿地中的分布及代谢途径尚未知。【目的】分析扎龙盐碱湿地未培养甲烷古菌RCII类群的多样性、推测产甲烷代谢途径及其潜在的盐碱适应机制。【方法】16S rRNA基因扩增子测序分析扎龙湿地土壤中甲烷古菌群组成；构建16S rRNA基因克隆文库分析扎龙湿地土壤RCII的多样性；宏基因组分析推测RCII古菌编码的产甲烷途径及与耐盐碱相关物质的合成基因。【结果】16S rRNA基因高通量测序发现未培养甲烷古菌的RCII类群占扎龙盐碱湿地总甲烷古菌的13.280%±0.019%；系统发育学分析表明该湿地的RCII由3个分支组成；宏基因组分析组装了2个优势的未培养RCII的基因组，均含完整的氢还原二氧化碳产甲烷途径的基因，并编码海藻糖的转运与合成基因。【结论】扎龙盐碱湿地土壤富含未培养RCII甲烷古菌，推测它们通过氢还原二氧化碳产甲烷，利用细胞内高的海藻糖适应盐碱环境。

关键词:盐碱湿地;甲烷古菌;Rice Cluster II;宏基因组;海藻糖

Abstract:

[Background] Wetlands harbobring a variety of methane-producing archaea emit ample methane. The uncultured methanogens, Rice Cluster II (RCII), exist widely in cold acidic peatlands, freshwater lake wetlands, minerotrophic fens, and northern peat moss. However, the distribution and metabolic pathways of RCII in the low-temperature saline-alkaline wetlands remain unknown. [Objective] To investigate the diversity and infer the methanogenic pathways and potential adaptation mechanisms of RCII in saline-alkaline Zhalong wetland. [Methods] High-throughput sequencing of the 16S rRNA genes in the top layer of soil was performed to reveal the composition of methanogenic archaea. We established the 16S rRNA gene clone library to analyze the phylogenetic clusters of RCII. We then conducted metagenomic analysis to infer the methanogenic pathways and the possible saline-alkaline adaption mechanisms of the RCII in Zhalong wetland.[Results] The uncultured RCII methanogens accounted for 13.280%±0.019% of the total methanogenic archaea in Zhalong wetland and were clustered into three phylogenetic groups. Two metagenome-assembled genomes of RCII possessed the complete suite of genes involved in methanogenesis via reduction of carbon dioxide. Furthermore, the two RCII genomes contained the genes associated with the transport and synthesis of trehalose. [Conclusion] Abundant uncultured RCII methanogens inhabit the saline-alkaline Zhalong wetland, and they can produce methane by reducing carbon dioxide and use the compatible solute trehalose to adapt to the saline-alkaline environment.

Key words:saline-alkaline wetland;methanogenic archaea;Rice Cluster Ⅱ;metagenome;trehalose