Table_2_Bacterial Communities Show Algal Host (Fucus spp.)/Zone Differentiation Across the Stress Gradient of the Intertidal Zone.xlsx

The intertidal zone often has varying levels of environmental stresses (desiccation, temperature, light) that result in highly stress-tolerant macrobiota occupying the upper zone while less tolerant species occupy the lower zone, but little comparative information is available for intertidal bacteria. Here we describe natural (unmanipulated) bacterial communities of three Fucus congeners (F. spiralis, high zone; F. vesiculosus, mid zone; F. distichus, low zone) as well as those of F. vesiculosus transplanted to the high zone (Dry and Watered treatments) and to the mid zone (Procedural Control) during summer in Maine (United States). We predicted that bacterial communities would be different among the differently zoned natural congeners, and that higher levels of desiccation stress in the high zone would cause bacterial communities of Dry transplants to become similar to F. spiralis, whereas relieving desiccation stress on Watered transplants would maintain the mid-zone F. vesiculosus bacterial community. Bacteria were identified as amplicon sequence variants (ASVs) after sequencing the V4 hypervariable region of the 16S rRNA gene. Microbiome composition and structure were significantly different between the differently zoned congeners at each tissue type (holdfasts, receptacles, vegetative tips). ASVs significantly associated with the mid-zone congener were frequently also present on the high-zone or low-zone congener, whereas overlap in ASVs between the high-zone and low-zone congeners was rare. Only 7 of 6,320 total ASVs were shared among tissues over all congeners and transplant treatments. Holdfast bacterial community composition of Dry transplants was not significantly different from that of F. spiralis, but Watered holdfast communities were significantly different from those of F. spiralis and not significantly different from those of procedural controls. Additional stressor(s) appeared important, because bacterial communities of Dry and Watered transplants were only marginally different from each other (p = 0.059). The relative abundance of Rhodobacteraceae associated with holdfasts generally correlated with environmental stress with highest abundance associated with F. spiralis and the two high-zone transplant treatments. These findings suggest that the abiotic stressors that shape distributional patterns of host species also affect their bacterial communities.

潮间带通常存在不同程度的环境胁迫（干燥脱水、温度、光照），这使得高潮带栖息着耐胁迫能力极强的大型生物，而耐受力较弱的物种则分布于低潮带，但目前针对潮间带细菌的比较研究信息却十分匮乏。本研究针对美国缅因州夏季的3种墨角藻属（Fucus）同属物种——螺旋墨角藻（F. spiralis，分布于高潮带）、泡叶墨角藻（F. vesiculosus，分布于中潮带）、二列墨角藻（F. distichus，分布于低潮带）的自然（未人工干预）细菌群落，以及移植至高潮带的泡叶墨角藻（设置干燥组与浇水组处理）、移植至中潮带的泡叶墨角藻（程序性对照）的细菌群落进行了表征。我们提出如下假说：不同潮带分布的自然同属物种的细菌群落存在显著差异；高潮带更强的干燥脱水胁迫会使干燥组移植样本的细菌群落结构趋近于螺旋墨角藻，而浇水组通过缓解干燥脱水胁迫，则可维持中潮带泡叶墨角藻的细菌群落特征。通过对16S rRNA基因的高变V4区进行测序，我们将细菌鉴定为扩增子序列变体（amplicon sequence variants, ASVs）。分析结果显示，在每种组织类型（固着器、生殖托、营养枝）中，不同潮带分布的墨角藻同属物种的微生物组组成与结构均存在显著差异。与中潮带物种显著相关的扩增子序列变体，通常也可在高潮带或低潮带物种中检出，但高潮带与低潮带物种之间的扩增子序列变体重叠却十分罕见。在所有同属物种与移植处理的所有组织中，6320个总扩增子序列变体中仅有7个是共有的。干燥组移植样本的固着器细菌群落组成与螺旋墨角藻无显著差异，但浇水组移植样本的固着器细菌群落则与螺旋墨角藻存在显著差异，且与程序性对照无显著差异。此外，其他胁迫因子似乎也发挥了作用，因为干燥组与浇水组移植样本的细菌群落仅存在边际显著差异（p = 0.059）。固着器相关的红杆菌科（Rhodobacteraceae）的相对丰度通常与环境胁迫程度呈正相关，在螺旋墨角藻以及两种高潮带移植处理组中丰度最高。本研究结果表明，塑造宿主物种分布格局的非生物胁迫因子，同样会影响其共生细菌群落。