Nitrogen Cycling of Active Bacteria within Oligotrophic Sediment of the Mid-Atlantic Ridge Flank

ABSTRACT Microbial ecology within oligotrophic marine sediment is poorly understood, yet is critical for understanding geochemical cycles. Here, 16S rRNA sequences from RNA and DNA inform the structure of active and total microbial communities in oligotrophic sediment on the western flank of the Mid-Atlantic Ridge. Sequences identified as Bacillariophyta chloroplast were detected within DNA, but undetectable within RNA, suggesting preservation in 5.6-million-year-old sediment. Statistical analysis revealed that RNA-based microbial populations correlated significantly with nitrogen concentrations, whereas DNA-based populations did not correspond to measured geochemical analytes. Bioenergetic calculations determined which metabolisms could yield energy in situ, and found that denitrification, nitrification, and nitrogen fixation were all favorable. A metagenome was produced from one sample, and included genes mediating nitrogen redox processes. Nitrogen respiration by active bacteria is an important metabolic strategy in North Pond sediments, and could be widespread in the oligotrophic sedimentary biosphere.

摘要 贫营养海洋沉积物中的微生物生态学了解甚少，但对于理解地球化学循环至关重要。在此，来自RNA和DNA的16S rRNA序列揭示了大西洋中脊西翼贫营养沉积物中活性和总微生物群落的结构。被鉴定为硅藻门叶绿体的序列在DNA中可检测到，但在RNA中无法检测到，这表明其在560万年历史的沉积物中得以保存。统计分析显示，基于RNA的微生物种群与氮浓度显著相关，而基于DNA的种群与所测地球化学分析物不对应。生物能量计算确定了哪些代谢在原地能够产生能量，并发现反硝化作用、硝化作用和固氮作用都是有利的。从一个样本中获得了宏基因组，其中包括介导氮氧化还原过程的基因。活性细菌的氮呼吸是北塘沉积物中一种重要的代谢策略，并且可能在贫营养沉积生物圈中广泛存在。