Abstract

Gammaproteobacteria from the family Endozoicomonadaceae have emerged as widespread associates of dense marine animal communities. Their abundance in coral reefs involves symbiotic relationships and possibly host nutrition. We explored functions encoded in the genome of an uncultured Endozoicomonadaceae ‘Candidatus Acestibacter aggregatus’ that lives inside gill cells of large Acesta excavata clams in deep-water coral reefs off mid-Norway. The dominance and deep branching lineage of this symbiont was confirmed using 16S rRNA gene sequencing and phylogenomic analysis from shotgun sequencing data. The 4.5 Mb genome binned in this study has a low GC content of 35% and is enriched in transposon and chaperone gene annotations indicating ongoing adaptation. Genes encoding functions potentially involved with the symbiosis include ankyrins, repeat in toxins, secretion, and nutritional systems. Complete pathways were identified for the synthesis of eleven amino acids and six B-vitamins. A minimal chitinolytic machinery was indicated from a glycosyl hydrolase GH18 and a lytic polysaccharide monooxygenase LPMO10. Expression of the latter was confirmed using proteomics. Signal peptides for secretion were identified for six polysaccharide degrading enzymes, ten proteases and three lipases. Our results suggest a nutritional symbiosis fuelled by enzymatic products from extracellular degradation processes.

中文翻译：

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蛤蜊鳃中的内生单胞菌科共生体编码必需营养素和多糖降解的基因

摘要

来自内生单胞菌科的 Gammaproteobacteria 已成为密集海洋动物群落的广泛伙伴。它们在珊瑚礁中的丰富性涉及共生关系和可能的宿主营养。我们探索了一种未培养的内生单胞菌科“ Candidatus Acestibacter aggregatus”的基因组中编码的功能，它生活在大型Acesta excavata的鳃细胞内挪威中部深水珊瑚礁中的蛤蜊。使用 16S rRNA 基因测序和鸟枪测序数据的系统基因组分析证实了这种共生体的优势和深分支谱系。本研究中合并的 4.5 Mb 基因组具有 35% 的低 GC 含量，并且富含转座子和伴侣基因注释，表明正在进行适应。编码可能与共生有关的功能的基因包括锚蛋白、毒素中的重复、分泌和营养系统。确定了合成 11 种氨基酸和 6 种 B 族维生素的完整途径。糖基水解酶 GH18 和裂解多糖单加氧酶 LPMO10 表明了最小的几丁质分解机制。使用蛋白质组学证实了后者的表达。为六种多糖降解酶、十种蛋白酶和三种脂肪酶鉴定了分泌信号肽。我们的研究结果表明，细胞外降解过程中的酶产物促进了营养共生。