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.已知深海热液喷口管状蠕虫的化能自养共生体（Chemoautotrophic symbionts）可为宿主提供全部基础营养。尽管已有研究探讨了化能自养共生体如何为共生体系提供氮源，但针对共生体氮代谢是否随环境条件变化的研究仍相对较少。脊管虫（Ridgeia piscesae）在东北太平洋热液喷口区域繁盛，占据多种微生境，并表现出高度的形态可塑性——例如长瘦型（long-skinny, LS）和短胖型（short-fat, SF）表型——这可能与环境条件相关。这种可塑性为研究共生体氮代谢是否随宿主表型差异发生变化提供了契机。研究人员从轴海山（Axial）与主奋进热液场（Main Endeavour Field）采集了长瘦型与短胖型R. piscesae个体。对脊管虫血液中的硝酸盐与铵盐进行了定量检测，并对宿主鳃羽组织以及含共生体组织中关键氮代谢基因的表达水平与稳定氮同位素比值进行了定量分析。两种表型的脊管虫血液中均含有丰富的硝酸盐与铵盐，但令人矛盾的是，环境铵盐浓度最低的个体，其血液铵盐浓度反而最高。同化型硝酸还原酶（Assimilatory nitrate reductase）的转录本始终未被检出，但无论是长瘦型还是短胖型R. piscesae的共生体中，均观察到异化型硝酸还原酶（dissimilatory nitrate reductase）基因以及共生体与宿主的铵同化基因的表达水平显著上调。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，长瘦型与短胖型脊管虫的共生体在不同程度上同时进行异化型硝酸还原与铵同化过程。由此可见，共生体氮代谢主要由环境条件而非宿主表型决定。