Molecular phylogeny suggests the affinity of the planktonic diatoms <i>Climacodium</i> and <i>Bellerochea</i> (Lithodesmiales, Mediophyceae)

<i>Climacodium frauenfeldianum</i> is a planktonic chain-forming diatom able to proliferate in severely oligotrophic waters of tropical seas. In this study, a strain of <i>C. frauenfeldianum</i>, the type of <i>Climacodium</i>, was established in culture from the tropical southwestern Atlantic Ocean off Brazil. SEM observations showed weakly silicified cells, without visible surface sculpturing. In the small subunit (SSU) rRNA and ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (<i>rbc</i>L) gene phylogeny, <i>C. frauenfeldianum</i> clustered with sequences of <i>Bellerochea malleus</i> (the type of <i>Bellerochea</i>) and <i>B. horologicalis</i>. Contrary to previous classifications that placed <i>Climacodium</i> in the Hemiaulaceae, <i>Climacodium</i> and <i>Bellerochea</i> should be placed in the same family, Bellerocheaceae. The species <i>Bellerochea yucatanensis</i> needs further research because sequences of the single strain available clustered with the genus <i>Lithodesmioides</i>. In adaptation to the oligotrophic open ocean environment, <i>C. frauenfeldianum</i> seems to have evolved an appearance closer to <i>Hemiaulus</i>, i.e. very lightly silicified flat cells with long elevations, and with diazotrophic cyanobionts.<i>Climacodium frauenfeldianum</i> 是一种营链状群体生活的浮游硅藻，能够在热带海域的严重贫营养水体中大量增殖。本研究从巴西邻近的西南大西洋热带海域成功分离培养了<i>Climacodium frauenfeldianum</i>菌株，该菌株为<i>Climacodium</i>属的模式菌株。扫描电子显微镜（Scanning Electron Microscope，SEM）观察结果显示，其细胞硅质化程度较弱，无可见的表面纹饰。基于小亚基核糖体RNA（SSU rRNA）基因与核酮糖-1,5-二磷酸羧化酶/加氧酶大亚基（<i>rbc</i>L）基因构建的系统发育分析显示，<i>Climacodium frauenfeldianum</i>与<i>Bellerochea malleus</i>（<i>Bellerochea</i>属的模式物种）及<i>B. horologicalis</i>的序列聚为一支。与此前将<i>Climacodium</i>归入半管藻科（Hemiaulaceae）的分类方案相悖，<i>Climacodium</i>与<i>Bellerochea</i>应当被归入同一科——波门藻科（Bellerocheaceae）。<i>Bellerochea yucatanensis</i>的分类地位尚需进一步研究，因目前仅有的单株序列与<i>Lithodesmioides</i>属的序列聚为一支。为适应贫营养的开阔大洋环境，<i>Climacodium frauenfeldianum</i>似乎演化出了与<i>Hemiaulus</i>（半管藻属）更为接近的形态特征：即硅质化程度极低的扁平细胞，带有长突起，且其体内携带固氮蓝藻共生体。

搜集汇总

背景与挑战

背景概述

该数据集基于分子系统发育分析（SSU rRNA和rbcL基因），研究了浮游硅藻Climacodium和Bellerochea的亲缘关系，结果表明它们应归入同一科Bellerocheaceae，而非之前分类的Hemiaulaceae。研究还探讨了这些硅藻在寡营养海洋环境中的适应特征，如弱硅化细胞和与固氮蓝细菌的共生。数据集覆盖生物物理学、微生物学和进化生物学等多个领域，关键词包括Bacillariophyceae和分子系统发育学。