Marine microbial communities from the sediments and bottom water in a productive coastal zone of the eastern South Pacific

Coastal zone off central Chile is characterized by high productivity associated with seasonal upwelling of nutrient rich water, but also by oxygen deficient waters. These oceanographic conditions favor the export of fresh organic matter towards deeper portions of the water column influencing microbial communities and biogeochemical conditions in the water column. Herein, we studied the dynamic of bacteria and archaea composition in the sediments and overlying water (16Sr RNA gene i-tag) and active functional nitrifying groups (qPCR) contribution in the water column during contrasting seasons. Also, oceanographic and biogeochemical conditions in the water and sediments were studied. Biogeochemical conditions presented the influence of oxygen deficient waters and the effects of ENSO during 2015 late fall. 60 phyla were detected to be present at the sediment and active in the bottom water, benthic microbial communities' composition at phyla level shared a higher similarity compared with bottom water counterparts. Archaea (Thaumarchaeota, Euryarchaeota, Lokiarchaeota contributed >12% to the dissimilarity found among the different biomes, followed by Marinimicrobia and Nitrospinae. The contribution of active nitrifyiers, ammonia oxidizing microorganisms (archaea and bacteria) and Nitrospina sp presented a greater contribution associated with winter and late fall consisting with higher oxygenation and nutrients in bottom waters. Oxygenation generate significant changes in the water column, particularly in bottom water active microbial communities related with nitrogen cycling.

智利中部近岸海域以高生产力为典型特征，该特征与富含营养盐的季节性上升流密切相关，同时该海域还存在缺氧水体。此类海洋学条件会促进新鲜有机质向水体深层输送，进而影响水体中的微生物群落与生物地球化学环境。本研究针对不同季节，对沉积物及上覆水中细菌与古菌的群落组成动态（通过16S rRNA基因扩增子（i-tag）测序），以及水体中活性功能硝化菌群（通过实时定量聚合酶链式反应（qPCR）定量）的贡献度展开了探究；同时还对水体与沉积物中的海洋学及生物地球化学特征进行了调查。研究结果显示，生物地球化学特征体现了2015年深秋时节缺氧水体的影响，以及厄尔尼诺-南方涛动（ENSO）的作用效果。本研究在沉积物与底层水中共检出60个菌门，且底栖微生物群落在门分类水平上的组成与底层水微生物群落的相似度更高。古菌（奇古菌门Thaumarchaeota、广古菌门Euryarchaeota、洛基古菌门Lokiarchaeota）对不同生境间的群落差异贡献度超过12%，紧随其后的类群为Marinimicrobia与Nitrospinae。活性硝化菌、氨氧化微生物（古菌与细菌）以及Nitrospina sp.的贡献度在冬季与深秋时节更高，这与底层水中更高的溶氧水平及营养盐含量相吻合。溶氧水平对水体环境产生了显著影响，尤其是与氮循环相关的底层水活性微生物群落。