Complex Microbial Communities Drive Iron and Sulfur Cycling in Arctic Fjord Sediments
Complex Microbial Communities Drive Iron and Sulfur Cycling in Arctic Fjord Sediments
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DOI：
10.1128/aem.00949-19
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发表时间：
2019-07-01
影响因子：
4.4
通讯作者：
Lloyd, K. G.
中科院分区：
文献类型：
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作者：
Buongiorno, J.;Herbert, L. C.;Lloyd, K. G.
冰川退缩正在改变北极的生物地球化学循环，那里的冰川径流为洋架初级生产力提供了铁。我们假设，在斯瓦尔巴特峡湾，微生物催化低有机质沉积物中强烈的铁和硫循环。这是因为低有机物限制了硫化物的生成，使铁可以移动到水柱中，而不是以单硫化铁的形式沉淀。在这项研究中，我们在斯瓦尔巴特群岛Van Keulenfjorden的两个地点上20厘米的高深度分辨率16S rRNA基因库中对此进行了测试。在靠近冰川的地方，12厘米深处有大量的还原铁硫化单胞菌、氧化铁的加利奥氏菌和马里奥氏菌，以及氧化硫磺的硫代三氯菌和变形杆菌。在此深度以下，硫酸盐还原脱硫菌科和脱硫球菌科的相对丰度增加。在外站，从铁循环分支向硫酸盐还原体的转变发生在较浅的深度(约5 cm)，对应较高的硫酸盐还原速率。相对活性有机质(用增量C-13和C/N比表示)在这个外部位置更为丰富，排序分析表明这影响了表层沉积物中的微生物群落结构。网络分析揭示了预测的铁和硫循环分类群与冰川附近未培养的分支之间的更多相关性。综上所述，这些结果表明，复杂的微生物群落催化铁和硫的氧化还原循环，特别是在靠近冰川的地方，那里的硫酸盐还原由于有机质的低可用性而受到限制。上层沉积物中硫酸盐还原的减弱使铁能够流入上覆水，在那里它可能被输送到大陆架。重要的是，冰川径流是北极初级生产的关键铁来源。在斯瓦尔巴群岛的峡湾，冰川退缩预计会刺激浮游植物的繁殖，而以前只限于外围边缘。沉积物输出量的减少和初级生产量的增加被假设为改变了沉积物的生物地球化学，其中任何可能被输送到陆架的游离还原铁将被微生物硫酸盐还原产生的硫化物埋藏起来。我们用测序数据支持这一假设，这些数据显示，随着距离斯瓦尔巴特群岛Van Keulenfjorden冰川的距离增加，硫酸盐还原类群和硫酸盐还原速率的相对丰度增加。群落结构是由有机地球化学驱动的，这表明随着冰川的继续消退，有机物质的增加输入将刺激峡湾内部沉积物中硫酸盐的还原。
Glacial retreat is changing biogeochemical cycling in the Arctic, where glacial runoff contributes iron for oceanic shelf primary production. We hypothesize that in Svalbard fjords, microbes catalyze intense iron and sulfur cycling in low-organic-matter sediments. This is because low organic matter limits sulfide generation, allowing iron mobility to the water column instead of precipitation as iron monosulfides. In this study, we tested this with high-depth-resolution 16S rRNA gene libraries in the upper 20 cm at two sites in Van Keulenfjorden, Svalbard. At the site closer to the glaciers, iron-reducing Desulfuromonadales, iron-oxidizing Gallionella and Mariprofundus, and sulfur-oxidizing Thiotrichales and Epsilonproteobacteria were abundant above a 12-cm depth. Below this depth, the relative abundances of sequences for sulfate-reducing Desulfobacteraceae and Desulfobulbaceae increased. At the outer station, the switch from iron-cycling clades to sulfate reducers occurred at shallower depths (similar to 5 cm), corresponding to higher sulfate reduction rates. Relatively labile organic matter (shown by delta C-13 and C/N ratios) was more abundant at this outer site, and ordination analysis suggested that this affected microbial community structure in surface sediments. Network analysis revealed more correlations between predicted iron-and sulfur-cycling taxa and with uncultured clades proximal to the glacier. Together, these results suggest that complex microbial communities catalyze redox cycling of iron and sulfur, especially closer to the glacier, where sulfate reduction is limited due to low availability of organic matter. Diminished sulfate reduction in upper sediments enables iron to flux into the overlying water, where it may be transported to the shelf.IMPORTANCE Glacial runoff is a key source of iron for primary production in the Arctic. In the fjords of the Svalbard archipelago, glacial retreat is predicted to stimulate phytoplankton blooms that were previously restricted to outer margins. Decreased sediment delivery and enhanced primary production have been hypothesized to alter sediment biogeochemistry, wherein any free reduced iron that could potentially be delivered to the shelf will instead become buried with sulfide generated through microbial sulfate reduction. We support this hypothesis with sequencing data that showed increases in the relative abundance of sulfate reducing taxa and sulfate reduction rates with increasing distance from the glaciers in Van Keulenfjorden, Svalbard. Community structure was driven by organic geochemistry, suggesting that enhanced input of organic material will stimulate sulfate reduction in interior fjord sediments as glaciers continue to recede.