DataSheet1.XLSX

During the Deepwater Horizon (DWH) oil spill, massive quantities of oil were deposited on the seafloor via a large-scale marine oil-snow sedimentation and flocculent accumulation (MOSSFA) event. The role of chemical dispersants (e.g., Corexit) applied during the DWH oil spill clean-up in helping or hindering the formation of this MOSSFA event are not well-understood. Here, we present the first experiment related to the DWH oil spill to specifically investigate the relationship between microbial community structure, oil and Corexit®, and marine oil-snow in coastal surface waters. We observed the formation of micron-scale aggregates of microbial cells around droplets of oil and dispersant and found that their rate of formation was directly related to the concentration of oil within the water column. These micro-aggregates are potentially important precursors to the formation of larger marine oil-snow particles. Therefore, our observation that Corexit® significantly enhanced their formation suggests dispersant application may play a role in the development of MOSSFA events. We also observed that microbial communities in marine surface waters respond to oil and oil plus Corexit® differently and much more rapidly than previously measured, with major shifts in community composition occurring within only a few hours of experiment initiation. In the oil-amended treatments without Corexit®, this manifested as an increase in community diversity due to the outgrowth of several putative aliphatic- and aromatic-hydrocarbon degrading genera, including phytoplankton-associated taxa. In contrast, microbial community diversity was reduced in mesocosms containing chemically dispersed oil. Importantly, different consortia of hydrocarbon degrading bacteria responded to oil and chemically dispersed oil, indicating that functional redundancy in the pre-spill community likely results in hydrocarbon consumption in both undispersed and dispersed oils, but by different bacterial taxa. Taken together, these data improve our understanding of how dispersants influence the degradation and transport of oil in marine surface waters following an oil spill and provide valuable insight into the early response of complex microbial communities to oil exposure.在深水地平线（DWH）油井泄漏事故期间，大量石油通过大规模海洋油雪沉积与絮状物聚集事件（MOSSFA）沉积于海底。目前，针对该事故清污过程中施用的化学分散剂（如科瑞透Corexit）对MOSSFA事件形成的促进或抑制作用，学界尚未形成明确认知。本研究开展了首个针对深水地平线油井泄漏事故的实验，专门探究沿岸表层水体中微生物群落结构、石油与科瑞透®（Corexit®）及海洋油雪之间的关联。我们观测到，在石油与分散剂液滴周围形成了微米级微生物细胞聚集体，且其形成速率与水柱中石油浓度直接相关。这类微聚集体可能是更大尺寸海洋油雪颗粒形成的重要前驱体。因此，我们观测到科瑞透®（Corexit®）可显著促进这类聚集体的形成，这表明施用分散剂可能对MOSSFA事件的发生起到一定作用。我们还发现，海洋表层水体微生物群落对石油以及石油与科瑞透®混合体系的响应模式与以往研究报道的截然不同，且响应速度快得多：实验启动仅数小时内，群落组成便发生了显著变化。在未添加科瑞透®的石油处理组中，这种变化表现为群落多样性升高——这是由于数种被推测为脂族烃与芳香烃降解菌的菌属（包括与浮游植物相关的类群）大量增殖所致。与之相反，在含有化学分散处理石油的中型实验生态系（mesocosms）中，微生物群落多样性出现下降。值得注意的是，针对石油与化学分散处理石油，烃类降解细菌的菌群结构存在差异，这表明泄漏前的微生物群落中存在功能冗余：无论是未分散的石油还是经分散的石油，其烃类均可被降解，但降解的细菌类群各不相同。综上，本研究数据增进了我们对油泄漏后分散剂如何影响海洋表层水体中石油降解与迁移过程的理解，并为复杂微生物群落对石油暴露的早期响应提供了宝贵的认知视角。