Some deep-sea chemosynthetic invertebrates and their symbiotic bacteria can use molecular hydrogen (H2) as their energy source. However, how much the chemosynthetic holobiont (endosymbiont-host association) physiologically depends on H2 oxidation has not yet been determined. Here, we demonstrate that the Campylobacterota endosymbionts of the gastropod Alviniconcha marisindica in the Kairei and Edmond fields (kAlv and eAlv populations, respectively) of the Indian Ocean, utilize H2 in response to their physical and environmental H2 conditions, although the 16S rRNA gene sequence of both the endosymbionts shared 99.6% identity. A thermodynamic calculation using in situ H2 and hydrogen sulfide (H2S) concentrations indicated that chemosynthetic symbiosis could be supported by metabolic energy via H2 oxidation, particularly for the kAlv holobiont. Metabolic activity measurements showed that both the living individuals and the gill tissues consumed H2 and H2S at similar levels. Moreover, a combination of fluorescence in situ hybridization, quantitative transcript analyses, and enzymatic activity measurements showed that the kAlv endosymbiont expressed the genes and enzymes for both H2- and sulfur-oxidations. These results suggest that both H2 and H2S could serve as the primary energy sources for the kAlv holobiont. The eAlv holobiont had the ability to utilize H2, but the gene expression and enzyme activity for hydrogenases were much lower than for sulfur-oxidation enzymes. These results suggest that the energy acquisitions of A. marisindica holobionts are dependent on H2- and sulfur-oxidation in the H2-enriched Kairei field and that the mechanism of dual metabolism is controlled by the in situ H2 concentration.

中文翻译：

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化学合成蜗牛Alviniconcha marisindica中的弯曲杆菌内共弯曲菌的双重能量代谢。

一些深海化学合成的无脊椎动物及其共生细菌可以使用分子氢（H2）作为能源。但是，尚未确定多少化学合成的盐铁（内共生体-宿主缔合）在生理上取决于H2氧化。在这里，我们证明了印度洋Kairei和Edmond田（分别为kAlv和eAlv种群）腹足纲Alviniconcha marisindica的弯曲杆菌内共生菌，尽管16S rRNA基因序列可利用H2响应其物理和环境H2条件。两种内共生菌具有99.6％的同一性。使用原位H2和硫化氢（H2S）浓度进行的热力学计算表明，化学合成共生可以通过H2氧化得到代谢能的支持，特别是对于kAlv全生命周期生物。代谢活性的测量表明，活人和腮组织都以相似的水平消耗了H2和H2S。此外，结合荧光原位杂交，定量转录分析和酶活性测量结果表明，kAlv内共生体表达了H2和硫氧化的基因和酶。这些结果表明，H2和H2S都可以用作kAlv盐环石的主要能源。eAlv holobiont具有利用H2的能力，但氢化酶的基因表达和酶活性远低于硫氧化酶。这些结果表明A的能量获取。