The marine sponge Halichondria panicea inhabits coastal areas around the globe and is a widely studied sponge species in terms of its biology, yet the ecological functions of its dominant bacterial symbiont 'Candidatus Halichondribacter symbioticus' remain unknown. Here, we present the draft genome of 'Ca. H. symbioticus' HS1 (2.8 Mbp, ca. 87.6% genome coverage) recovered from the sponge metagenome of H. panicea in order to study functions and symbiotic interactions at the genome level. Functional genome comparison of HS1 against closely related free-living seawater bacteria revealed a reduction of genes associated with carbohydrate transport and transcription regulation, pointing towards a limited carbohydrate metabolism, and static transcriptional dynamics reminiscent of other bacterial symbionts. In addition, HS1 was enriched in sponge symbiont specific gene families related to host-symbiont interactions and defence. Similarity in the functional gene repertoire between HS1 and a phylogenetically more distant symbiont in the marine sponge Aplysina aerophoba, based on COG category distribution, suggest a convergent evolution of symbiont specific traits and general metabolic features. This warrants further investigation into convergent genomic evolution of symbionts across different sponge species and habitats.

中文翻译：

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海绵共生体'Candidatus Halichondribacter symbioticus'的基因组分析表明，基因组适应于依赖宿主的生活方式。

海洋海绵哈氏钩虫生活在全球沿海地区，就其生物学而言，是一种被广泛研究的海绵物种，但其主要细菌共生体“共生梭状芽孢杆菌”的生态功能仍然未知。在这里，我们介绍了'Ca的基因组草图。为了从基因组水平研究功能和共生相互作用，从H. panicea的海绵状基因组中回收了H. symbioticus的HS1（2.8 Mbp，基因组覆盖率约87.6％）。HS1与密切相关的自由活动海水细菌的功能基因组比较显示，与碳水化合物运输和转录调控有关的基因减少，表明碳水化合物代谢有限，静态转录动力学使人联想到其他细菌共生体。此外，HS1富含与宿主共生体相互作用和防御相关的海绵共生体特异性基因家族。基于COG类别分布，HS1与海洋海绵状拟杆菌中系统发育距离较远的共生体之间的功能基因表集相似，表明共生体特定性状和一般代谢特征的趋同演化。这值得进一步研究共生体在不同海绵物种和生境中的趋同基因组进化。提示共生体特定性状和一般代谢特征的趋同进化。这值得进一步研究共生体在不同海绵物种和生境中的趋同基因组进化。提示共生体特定性状和一般代谢特征的趋同进化。这值得进一步研究共生体在不同海绵物种和生境中的趋同基因组进化。