Data from: Microbe biogeography tracks water-masses in a dynamic oceanic frontal system

Dispersal limitation, not just environmental selection, plays an important role in microbial biogeography. The distance-decay relationship is thought to be weak in habitats where dispersal is high, such as in the pelagic environment, where ocean currents facilitate microbial dispersal. Most studies of microbial community composition to date have observed little geographical heterogeneity on a regional scale (100s km). We present a study of microbial communities across a dynamic frontal zone in the South West Indian Ocean and investigate the spatial structure of the microbes with respect to the different water masses separated by these fronts. We collected 153 samples of free-living microorganisms from five seamounts located along a gradient from subtropical to subantarctic waters and across three depth layers, 1) the sub-surface chlorophyll maximum (c. 40m), 2) the bottom of the euphotic zone (c. 200m), and 3) the benthic boundary layer (300-2000m). Diversity and abundance of microbial operational taxonomic units (OTUs) was assessed by amplification and sequencing of the 16S rRNA gene on an Illumina MiSeq platform. Multivariate analyses showed that microbial communities were structured more strongly by depth than by latitude, with similar phyla occurring within each depth stratum across seamounts. The deep layer was homogeneous across the entire survey area, corresponding to the spread of Antarctic intermediate water. However, within both the sub-surface layer and the intermediate depth stratum there was evidence for OTU turnover across fronts. The microbiome of these layers appears to be divided into three distinct biological regimes corresponding to the subantarctic surface water, the convergence zone, and subtropical. We show that microbial biogeography across depth and latitudinal gradients is linked to the water-masses the microbes persist in, resulting in regional patterns of microbial biogeography, that correspond to the regional scale physical oceanography.

扩散限制（dispersal limitation）而非仅环境选择，在微生物生物地理学中发挥着重要作用。学界普遍认为，在扩散能力较强的生境中，距离衰减关系（distance-decay relationship）较为微弱——例如远洋环境，海洋环流可促进微生物的扩散。迄今为止，多数针对微生物群落组成的研究在区域尺度（数百公里）上几乎未观测到显著的地理异质性。本研究针对西南印度洋横跨动态锋面区域的微生物群落展开研究，探究受这些锋面分隔的不同水团对应的微生物空间结构。我们沿亚热带至亚南极水域的梯度，在5座海山的三个深度层采集了153份自由生活微生物样本：1）表层下叶绿素最大值层（约40米）；2）真光层底部（约200米）；3）底栖边界层（300~2000米）。本研究通过Illumina MiSeq平台对16S rRNA基因进行扩增与测序，以此评估微生物操作分类单元（operational taxonomic units, OTUs）的多样性与丰度。多变量分析结果显示，微生物群落的构建受深度的影响远强于纬度，各海山相同深度层内的微生物门类组成相似。整个调查区域的深层水体群落组成均一，这与南极中层水的扩散特征相符。然而，在表层下与中层深度层中，均观测到OTU在锋面处发生群落更替的现象。上述两层的微生物组可划分为三个截然不同的生物群落类型，分别对应亚南极表层水、辐合带与亚热带水域。本研究证实，沿深度与纬度梯度分布的微生物生物地理学模式与微生物所处的水团密切相关，由此形成的区域微生物生物地理格局，与区域尺度的物理海洋学特征高度匹配。