Spatial and seasonal distribution of Thaumarchaeota in the water column and sediment of the southern North Sea

We have examined the spatial and seasonal distribution of Thaumarchaeota in the water column and sediment of the southern North Sea using the specific intact polar lipid (IPL) hexose, phosphohexose (HPH) crenarchaeol, as well as thaumarchaeotal 16S rRNA gene abundances and expression. In the water column, a higher abundance of Thaumarchaeota was observed in the winter season than in the summer, which is in agreement with previous studies, but this was not the case in the sediment where Thaumarchaeota were most abundant in spring and summer. This observation corresponds well with the idea that ammonia availability is a key factor in thaumarchaeotal niche determination. In the surface waters of the southern North Sea, we observed a spatial variability in HPH crenarchaeol, thaumarchaeotal 16S rRNA gene abundance and transcriptional activity that corresponded well with the different water masses present. In bottom waters, a clear differentiation based on water masses was not observed; instead, we suggest that observed differences in thaumarchaeotal abundance with depth may be related to resuspension from the sediment. This could be due to suspension of benthic Thaumarchaeota to the water column or due to delivery of e.g. resuspended sediment or ammonium to the water column, which could be utilized by pelagic Thaumarchaeota. This study has shown that the seasonality of Thaumarchaeota in water and sediment is different and highlights the importance of water masses, currents and sedimentary processes in determining the spatial abundance of Thaumarchaeota in the southern North Sea.

本研究以特异性完整极性脂（intact polar lipid, IPL）组分己糖、磷酸己糖（phosphohexose, HPH）型克雷拉古菌醇（crenarchaeol），以及奇古菌门（Thaumarchaeota）16S核糖体RNA基因的丰度与表达量为分析指标，系统探究了北海南部水柱与沉积物中奇古菌的空间及季节分布特征。在水柱中，奇古菌丰度在冬季显著高于夏季，该结果与既往研究共识相符；但沉积物中的奇古菌分布则呈现相反趋势，其丰度在春季与夏季达到峰值。这一观测结果与“氨可用性是决定奇古菌生态位的关键因素”这一科学假说高度契合。在北海南部表层水中，我们观测到HPH型克雷拉古菌醇含量、奇古菌16S核糖体RNA基因丰度及转录活性均存在空间异质性，且该异质性与区域内现存的不同水团密切相关；而在底层水中，未观测到基于水团的显著群落分化。据此我们推测，观测到的奇古菌丰度随深度的变化可能与沉积物的再悬浮过程有关，具体机制可分为两类：一是底栖奇古菌被悬浮至水柱中，二是再悬浮沉积物、铵盐等物质被输送至水柱，进而被浮游奇古菌利用。本研究表明，水体与沉积物中奇古菌的季节动态存在显著差异，并凸显了水团、洋流及沉积过程对北海南部奇古菌空间丰度分布的重要调控作用。