NSF Science & Technology Center for Coastal Margin Observation & Prediction (CMOP), Portland, OR, USA.
Institute of Environmental Health, Oregon Health & Science University, Portland, OR, USA.
Microbiologyopen. 2017 Dec;6(6). doi: 10.1002/mbo3.522. Epub 2017 Aug 6.
Estuarine turbidity maxima (ETM) function as hotspots of microbial activity and diversity in estuaries, yet, little is known about the temporal and spatial variability in ETM bacterial community composition. To determine which environmental factors affect ETM bacterial populations in the Columbia River estuary, we analyzed ETM bacterial community composition (Sanger sequencing and amplicon pyrosequencing of 16S rRNA gene) and bulk heterotrophic production ( H-leucine incorporation rates). We collected water 20 times to cover five ETM events and obtained 42 samples characterized by different salinities, turbidities, seasons, coastal regimes (upwelling vs. downwelling), locations, and particle size. Spring and summer populations were distinct. All May samples had similar bacterial community composition despite having different salinities (1-24 PSU), but summer non-ETM bacteria separated into marine, freshwater, and brackish assemblages. Summer ETM bacterial communities varied depending on coastal upwelling or downwelling conditions and on the sampling site location with respect to tidal intrusion during the previous neap tide. In contrast to ETM, whole (>0.2 μm) and free-living (0.2-3 μm) assemblages of non-ETM waters were similar to each other, indicating that particle-attached (>3 μm) non-ETM bacteria do not develop a distinct community. Brackish water type (ETM or non-ETM) is thus a major factor affecting particle-attached bacterial communities. Heterotrophic production was higher in particle-attached than free-living fractions in all brackish waters collected throughout the water column during the rise to decline of turbidity through an ETM event (i.e., ETM-impacted waters). However, free-living communities showed higher productivity prior to or after an ETM event (i.e., non-ETM-impacted waters). This study has thus found that Columbia River ETM bacterial communities vary based on seasons, salinity, sampling location, and particle size, with the existence of three particle types characterized by different bacterial communities in ETM, ETM-impacted, and non-ETM-impacted brackish waters. Taxonomic analysis suggests that ETM key biological function is to remineralize organic matter.
河口最大浑浊带（ETM）是河口微生物活动和多样性的热点，但对于 ETM 细菌群落组成的时空变异性知之甚少。为了确定哪些环境因素影响哥伦比亚河口的 ETM 细菌种群，我们分析了 ETM 细菌群落组成（16S rRNA 基因的 Sanger 测序和扩增子焦磷酸测序）和总异养生产力（H-亮氨酸掺入率）。我们共采集了 20 次水，以覆盖 5 次 ETM 事件，并获得了 42 个样本，这些样本具有不同的盐度、浊度、季节、沿海环境（上升流与下降流）、位置和粒径。春、夏两季的种群明显不同。尽管所有 5 月份的样本盐度不同（1-24 PSU），但其细菌群落组成相似，但夏季非 ETM 细菌则分为海洋、淡水和半咸水组合。夏季 ETM 细菌群落因沿海上升流或下降流条件以及前一次小潮期间潮汐入侵时的采样点位置而异。与 ETM 不同，非 ETM 水的整个（>0.2μm）和自由生活（0.2-3μm）组合彼此相似，表明颗粒附着（>3μm）的非 ETM 细菌没有形成独特的群落。因此，半咸水类型（ETM 或非 ETM）是影响颗粒附着细菌群落的主要因素。在整个水柱中收集的所有半咸水在浊度上升到下降过程中通过 ETM 事件（即受 ETM 影响的水）时，颗粒附着比自由生活部分的异养生产力更高。然而，在 ETM 事件之前或之后，自由生活群落表现出更高的生产力（即非 ETM 影响的水）。因此，本研究发现，哥伦比亚河 ETM 细菌群落根据季节、盐度、采样地点和粒径而变化，在 ETM、受 ETM 影响和非 ETM 影响的半咸水中存在三种颗粒类型，其特征是不同的细菌群落。分类分析表明，ETM 的主要生物学功能是矿化有机物。
