天山一号冰川前沿生态系统真菌群落结构演替及分布格局

【目的】分析真菌群落结构和多样性随着一号冰川退缩前沿年代序列的变化,揭示真菌群落的演替轨迹及环境因子对群落组成的影响。【方法】采用宏基因组学研究方法,结合生物信息学和统计学分析技术,对取自一号冰川末端表面冰尘,底部和前沿14个样品进行总DNA的提取,ITS基因的扩增并使用Illumina Miseq平台测序,通过相关生物地理化学特性综合分析在不同年代序列下真菌群落结构及其演替规律。【结果】经测序,筛选和质控分析获得185103条rawreads,占78.3%的非单序列在97%的相似度聚类分析共得到300个操作分类单元(OTU),共划分为6个门:子囊菌门(Ascomycota,52.7%)、担子菌门(Basidiomycota,16.9%)、壶菌门(Chytridiomycota,15.1%)、接合菌门(Zygomycota,2.4%)和球囊菌门(Glomeromycota,1.2%)。从演替初期到后期阶段虽然子囊菌的序列数逐渐下降而担子菌出现缓慢上升趋势,但子囊菌随着土壤年代序列的增加始终为优势类群,壶菌在冰川底部和前沿基层普遍存在且丰度仅次于子囊菌和担子菌。我们在缺乏植被的最新退缩基层发现依靠自养型宿主存活的活体营养菌,如Taphrinomycetes、Urediniomycetes和Ustilaginomycetes。从冰川底部和前沿基层检测到丰度较高的酵母菌,而粪生真菌(coprophilous fungi)仅仅出现在冰川前沿基层,共23个操作分类单元。球囊菌仅在前沿部分样品中存在,有着十分狭小的生态位分布。【结论】一号冰川前沿随着年代序列的增加真菌群落存在明显的演替轨迹和多样性的显著变化,不同生态位真菌类群组成的相似性较低且都存在明显的指示性真菌类群。     

Complete modification maps for the cytosolic small and large subunit rRNAs of Euglena gracilis: functional and evolutionary implications of contrasting patterns between the two rRNA components

In the protist Euglena gracilis, the cytosolic small subunit (SSU) rRNA is a single, covalently continuous species typical of most eukaryotes; in contrast, the large subunit (LSU) rRNA is naturally fragmented, comprising 14 separate RNA molecules instead of the bipartite (28S + 5.8S) eukaryotic LSU rRNA typically seen. We present extensively revised secondary structure models of the E. gracilis SSU and LSU rRNAs and have mapped the positions of all of the modified nucleosides in these rRNAs (88 in SSU rRNA and 262 in LSU rRNA, with only 3 LSU rRNA modifications incompletely characterized). The relative proportions of ribose-methylated nucleosides and pseudouridine (∼ 60% and ∼ 35%, respectively) are closely similar in the two rRNAs; however, whereas the Euglena SSU rRNA has about the same absolute number of modifications as its human counterpart, the Euglena LSU rRNA has twice as many modifications as the corresponding human LSU rRNA. The increased levels of rRNA fragmentation and modification in E. gracilis LSU rRNA are correlated with a 3-fold increase in the level of mispairing in helical regions compared to the human LSU rRNA. In contrast, no comparable increase in mispairing is seen in helical regions of the SSU rRNA compared to its homologs in other eukaryotes. In view of the reported effects of both ribose-methylated nucleoside and pseudouridine residues on RNA structure, these correlations lead us to suggest that increased modification in the LSU rRNA may play a role in stabilizing a ‘looser’ structure promoted by elevated helical mispairing and a high degree of fragmentation.