MD-178-3280 16S v4-v6 Targeted Locus (Loci). sediment metagenome

Assessing the impacts of methane released from hydrate-bearing environments on global carbon cycling would require detailed insights into the distributions and capacities of microbial communities at differ- ent horizons of sediment column. In this study, we conducted geochemical, gene abundance and diversity analyses for a sediment core retrieved from a potential hydrate-bearing region off southwestern Taiwan. Geochemical profiles were characterized by a sulfate-to-methane transition with decreasing total organic carbon and nitrogen in sediments, and increasing dissolved inorganic carbon, ammonium and total sulfur in sediments. Bacterial and archaeal 16S rRNA and amoA gene abundances decreased with depth. In con- trast, ANME-1 and -2 16S rRNA gene abundances increased significantly across the sulfate-to-methane transition and peaked at different horizons below this interface. A total of 124,379 bacterial and 130,351 archaeal reads were recovered through tag-pyrosequencing of 16S rRNA genes and categorized into 9014 bacterial and 6394 archaeal operational taxonomic units on the basis of 97% sequence similar- ity, respectively. Major bacterial phyla/divisions and archaeal groups (>5% of the total reads) detected included Chloroflexi, Planctomycetes, OP9, Deltaproteobacteria, BHI80-139, MBG-B, Halobacteria, MCG, Thermoplasmata, ANME-1 and MG-I. The abundance variations of most major OTUs (>0.5% of the total reads) were statistically correlated with those of geochemical parameters. These lines of evidence suggest that the populations represented by the major OTUs or detected by group-specific primers were compart- mentalized into different horizons and involved directly or indirectly in the cycling of methane, sulfate, organic carbon and nitrogen. Overall, this study demonstrates that the deep sequencing coverage com- bined with the quantification of gene abundance and geochemical characterization would enable to uncover the detailed distributions and potential metabolic capabilities of specific groups from complexly structured microbial communities in methane-rich marine sediments.

评估含天然气水合物环境（hydrate-bearing environments）释放的甲烷对全球碳循环的影响，需要深入了解沉积物柱（sediment column）不同层位的微生物群落分布与功能潜能。本研究针对台湾西南部海域一处潜在含天然气水合物区域获取的沉积物岩芯（sediment core），开展了地球化学、基因丰度及多样性分析。地球化学剖面以硫酸盐-甲烷转换带（sulfate-to-methane transition）为特征，沉积物中总有机碳（total organic carbon）、总氮含量随深度降低，而溶解无机碳（dissolved inorganic carbon）、铵态氮与总硫含量则随深度升高。细菌与古菌的16S rRNA基因及氨单加氧酶基因（amoA）丰度随深度呈下降趋势。与之相反，厌氧甲烷氧化古菌（ANME）-1与ANME-2的16S rRNA基因丰度在硫酸盐-甲烷转换带内显著升高，并在该界面下方的不同沉积层位达到峰值。通过16S rRNA基因标签焦磷酸测序（tag-pyrosequencing），共获得124379条细菌读段与130351条古菌读段，基于97%的序列相似性，分别将其聚类为9014个细菌操作分类单元（operational taxonomic unit，OTU）与6394个古菌操作分类单元。检测到的主要细菌门/类群与古菌类群（占总读段比例>5%）包括绿弯菌门（Chloroflexi）、浮霉菌门（Planctomycetes）、OP9、δ-变形菌纲（Deltaproteobacteria）、BHI80-139、MBG-B、盐杆菌纲（Halobacteria）、MCG、热原体纲（Thermoplasmata）、ANME-1与MG-I。绝大多数丰度占比>0.5%的主要操作分类单元的丰度变化，与地球化学参数的变化呈显著统计相关性。上述证据表明，由主要操作分类单元所代表的类群，或通过类群特异性引物（group-specific primers）检测到的类群，呈区域化分布于不同沉积层位，并直接或间接参与甲烷、硫酸盐、有机碳与氮的循环过程。总体而言，本研究表明，结合深度测序覆盖度（deep sequencing coverage）、基因丰度定量与地球化学表征，能够揭示富甲烷海洋沉积物中复杂结构微生物群落内特定类群的精细分布与潜在代谢功能。