Data from: Characterizing the plasticity of nitrogen metabolism by the host and symbionts of the hydrothermal vent chemoautotrophic symbioses Ridgeia piscesae

Chemoautotrophic symbionts of deep sea hydrothermal vent tubeworms are known to provide their hosts with all their primary nutrition. While studies have examined how chemoautotrophic symbionts provide the association with nitrogen, fewer have examined if symbiont nitrogen metabolism varies as a function of environmental conditions. Ridgeia piscesae tubeworms flourish at Northeastern Pacific vents, occupy a range of microhabitats, and exhibit a high degree of morphological plasticity [e.g. long-skinny (LS) and short-fat (SF) phenotypes] that may relate to environmental conditions. This plasticity affords an opportunity to examine whether symbiont nitrogen metabolism varies among host phenotypes. LS and SF R. piscesae were recovered from the Axial and Main Endeavour Field hydrothermal vents. Nitrate and ammonium were quantified in Ridgeia blood, and the expression of key nitrogen metabolism genes, as well as stable nitrogen isotope ratios, was quantified in host branchial plume and symbiont-containing tissues. Nitrate and ammonium were abundant in the blood of both phenotypes though environmental ammonium concentrations were, paradoxically, lowest among individuals with the highest blood ammonium. Assimilatory nitrate reductase transcripts were always below detection, though in both LS and SF R. piscesae symbionts, we observed elevated expression of dissimilatory nitrate reductase genes, as well as symbiont and host ammonium assimilation genes. Site-specific differences in expression, along with tissue stable isotope analyses, suggest that LS and SF Ridgeia symbionts are engaged in both dissimilatory nitrate reduction and ammonia assimilation to varying degrees. As such, it appears that environmental conditions –not host phenotype—primarily dictates symbiont nitrogen metabolism.

深海热液喷口（deep sea hydrothermal vent）管状蠕虫的化能自养共生体（chemoautotrophic symbionts）已被证实可为宿主提供全部初级营养。尽管已有研究探讨了化能自养共生体如何为共生联合体提供氮源，但针对共生体氮代谢是否随环境条件变化的研究仍相对匮乏。脊管虫（Ridgeia piscesae）繁盛栖息于东北太平洋热液喷口，占据多样微生境，且表现出高度的形态可塑性，例如细长型（long-skinny, LS）与短胖型（short-fat, SF）表型，该可塑性或与环境条件密切相关。这种形态可塑性为探究共生体氮代谢是否随宿主表型差异发生变化提供了绝佳研究契机。研究人员从轴海丘热液喷口（Axial）与主奋进区热液喷口（Main Endeavour Field）采集了LS、SF型脊管虫样本，随后对脊管虫体液中的硝酸盐与铵盐含量进行定量分析，并对宿主鳃羽组织及含共生体组织中的关键氮代谢基因表达量、稳定氮同位素比值开展定量检测。结果显示，两种表型脊管虫的体液中均含有丰富的硝酸盐与铵盐，但反常的是，体液铵盐含量最高的个体，其所处环境的铵盐浓度反而最低。同化型硝酸还原酶（assimilatory nitrate reductase）的转录本始终未被检出，然而无论是LS型还是SF型脊管虫的共生体，研究人员均观测到异化型硝酸还原酶（dissimilatory nitrate reductase）以及共生体与宿主的铵同化基因（ammonium assimilation genes）的表达量显著上调。基因表达的位点特异性差异结合组织稳定同位素分析结果表明，LS与SF型脊管虫的共生体在不同程度上同时进行异化型硝酸盐还原与铵同化过程。由此可见，共生体氮代谢主要由环境条件而非宿主表型所决定。