Few studies have thus far explored the microbiomes of glass sponges (Hexactinellida). The present study seeks to elucidate the composition of the microbiota associated with the glass sponge Vazella pourtalesii and the functional strategies of the main symbionts. We combined microscopic approaches with metagenome-guided microbial genome reconstruction and amplicon community profiling towards this goal. Microscopic imaging revealed that the host and microbial cells appeared within dense biomass patches that are presumably syncytial tissue aggregates. Based on abundances in amplicon libraries and metagenomic data, SAR324 bacteria, Crenarchaeota, Patescibacteria and Nanoarchaeota were identified as abundant members of the V. pourtalesii microbiome and their genomic potentials were thus analyzed in detail. A general pattern emerged in that the V. pourtalesii symbionts had very small genome sizes in the range of 0.5-2.2 Mb and low GC contents, even below those of seawater relatives. Based on functional analyses of metagenome-assembled genomes (MAGs), we propose two major microbial strategies: the 'givers', namely Crenarchaeota and SAR324, heterotrophs and facultative anaerobes, produce and partly secrete all required amino acids and vitamins. The 'takers', Nanoarchaeota and Patescibacteria, are anaerobes with reduced genomes that tap into the microbial community for resources, e.g., lipids and DNA, likely using pili-like structures. We posit that the existence of microbial cells in sponge syncytia together with the low-oxygen conditions in the seawater environment are factors that shape the unique compositional and functional properties of the microbial community associated with V. pourtalesii.

中文翻译：

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玻璃海绵Vazella pourtalesii中的微生物生存策略

迄今为止，很少有研究探索玻璃海绵的微生物组（Hexactinellida）。本研究试图阐明与玻璃海绵Vazella pourtalesii相关的微生物群的组成和主要共生体的功能策略。我们将微观方法与元基因组指导的微生物基因组重建和扩增子群落分析相结合，以实现这一目标。显微成像显示，宿主细胞和微生物细胞出现在致密的生物质斑块中，这些斑块可能是合胞体组织聚集体。根据扩增子文库中的丰度和宏基因组学数据，SAR324细菌，Crenarchaeota，Patecibacteria和Nanoarchaeota被确定为V. pourtalesii的丰富成员。因此详细分析了微生物组及其基因组潜力。一个普遍的模式出现在V. pourtalesii共生体具有很小的基因组大小，范围在0.5-2.2 Mb之间，GC含量低，甚至低于海水亲属。基于对元基因组组装基因组（MAG）的功能分析，我们提出了两种主要的微生物策略：“给予者”（即Crenarchaeota和SAR324），异养生物和兼性厌氧菌，可以产生并部分分泌所有必需的氨基酸和维生素。“摄入者”，即纳诺古菌和Patecibacteria，是具有减少的基因组的厌氧菌，可以利用菌毛样结构进入微生物群落获取资源，例如脂质和DNA。我们认为，海绵合胞体中微生物细胞的存在以及海水环境中的低氧条件是决定与之相关的微生物群落独特组成和功能特性的因素。V. pourtalesii。