Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark.
ISME J. 2012 Jun;6(6):1222-37. doi: 10.1038/ismej.2011.181. Epub 2011 Dec 1.
We assessed the microbial diversity and microenvironmental niche characteristics in the didemnid ascidian Lissoclinum patella using 16S rRNA gene sequencing, microsensor and imaging techniques. L. patella harbors three distinct microbial communities spatially separated by few millimeters of tunic tissue: (i) a biofilm on its upper surface exposed to high irradiance and O(2) levels, (ii) a cloacal cavity dominated by the prochlorophyte Prochloron spp. characterized by strong depletion of visible light and a dynamic chemical microenvironment ranging from hyperoxia in light to anoxia in darkness and (iii) a biofilm covering the underside of the animal, where light is depleted of visible wavelengths and enriched in near-infrared radiation (NIR). Variable chlorophyll fluorescence imaging demonstrated photosynthetic activity, and hyperspectral imaging revealed a diversity of photopigments in all microhabitats. Amplicon sequencing revealed the dominance of cyanobacteria in all three layers. Sequences representing the chlorophyll d containing cyanobacterium Acaryochloris marina and anoxygenic phototrophs were abundant on the underside of the ascidian in shallow waters but declined in deeper waters. This depth dependency was supported by a negative correlation between A. marina abundance and collection depth, explained by the increased attenuation of NIR as a function of water depth. The combination of microenvironmental analysis and fine-scale sampling techniques used in this investigation gives valuable first insights into the distribution, abundance and diversity of bacterial communities associated with tropical ascidians. In particular, we show that microenvironments and microbial diversity can vary significantly over scales of a few millimeters in such habitats; which is information easily lost by bulk sampling.
我们使用 16S rRNA 基因测序、微传感器和成像技术评估了碟形海鞘 Lissoclinum patella 的微生物多样性和微环境生态位特征。L. patella 拥有三个不同的微生物群落，它们在几毫米的套膜组织中空间分离：（i）其暴露在高辐照度和 O(2)水平下的上表面的生物膜，（ii）一个以原绿藻 Prochloron spp. 为主的泄殖腔腔，其特点是可见光和动态化学微环境强烈耗尽，光照下为过氧，黑暗下为缺氧，（iii）覆盖动物下侧的生物膜，那里的光耗尽了可见光波长，富含近红外辐射（NIR）。可变叶绿素荧光成像表明存在光合作用，高光谱成像揭示了所有微生境中多种光色素的多样性。扩增子测序表明，所有三个层中的优势类群均为蓝细菌。含有叶绿素 d 的蓝细菌 Acaryochloris marina 和缺氧光养生物的序列在浅水区的海鞘下侧丰富，但在较深的水域中减少。这种深度依赖性得到了 Acaryochloris marina 丰度与采集深度之间负相关的支持，这是由于 NIR 的衰减随着水深的增加而增加。本研究中使用的微环境分析和精细采样技术的结合，为与热带海鞘相关的细菌群落的分布、丰度和多样性提供了有价值的初步见解。特别是，我们表明，在这种栖息地中，微环境和微生物多样性可以在几毫米的尺度上发生显著变化；而这些信息是通过批量采样很容易丢失的。
