How the diverse bacterial communities inhabiting desert soils maintain energy and carbon needs is much debated. Traditionally, most bacteria are thought to persist by using organic carbon synthesized by photoautotrophs following transient hydration events. Recent studies focused on Antarctic desert soils have revealed, however, that some bacteria use atmospheric trace gases, such as hydrogen (H₂), to conserve energy and fix carbon independently of photosynthesis. In this study, we investigated whether atmospheric H₂ oxidation occurs in four nonpolar desert soils and compared this process to photosynthesis. To do so, we first profiled the distribution, expression, and activities of hydrogenases and photosystems in surface soils collected from the South Australian desert over a simulated hydration-desiccation cycle. Hydrogenase-encoding sequences were abundant in the metagenomes and metatranscriptomes and were detected in actinobacterial, acidobacterial, and cyanobacterial metagenome-assembled genomes. Native dry soil samples mediated H₂ oxidation, but rates increased 950-fold following wetting. Oxygenic and anoxygenic phototrophs were also detected in the community but at lower abundances. Hydration significantly stimulated rates of photosynthetic carbon fixation and, to a lesser extent, dark carbon assimilation. Hydrogenase genes were also widespread in samples from three other climatically distinct deserts, the Namib, Gobi, and Mojave, and atmospheric H₂ oxidation was also greatly stimulated by hydration at these sites. Together, these findings highlight that H₂ is an important, hitherto-overlooked energy source supporting bacterial communities in desert soils. Contrary to our previous hypotheses, however, H₂ oxidation occurs simultaneously rather than alternately with photosynthesis in such ecosystems and may even be mediated by some photoautotrophs.

中文翻译：

---

沙漠土壤中富含氢氧化细菌，并受到水合作用的强烈刺激


栖息在沙漠土壤中的不同细菌群落如何维持能源和碳需求存在很多争议。传统上，大多数细菌被认为是通过利用光合自养生物在短暂水合事件后合成的有机碳来生存的。然而，最近针对南极沙漠土壤的研究表明，一些细菌利用大气中的微量气体，例如氢气 (H ₂ )，来保存能量并固定碳，而无需进行光合作用。在本研究中，我们研究了四种非极地沙漠土壤中是否发生大气 H ₂氧化，并将该过程与光合作用进行了比较。为此，我们首先通过模拟水合-干燥循环，对从南澳大利亚沙漠收集的表层土壤中氢化酶和光系统的分布、表达和活性进行了分析。氢化酶编码序列在宏基因组和宏转录组中丰富，并在放线菌、酸杆菌和蓝藻宏基因组组装的基因组中检测到。原生干燥土壤样品介导 H ₂氧化，但润湿后速率增加了 950 倍。在群落中也检测到产氧和缺氧光养生物，但丰度较低。水合作用显着刺激了光合作用碳固定的速率，并在较小程度上刺激了暗碳同化的速率。氢化酶基因在其他三个气候不同的沙漠（纳米布、戈壁和莫哈韦沙漠）的样本中也广泛存在，并且这些地点的水合作用也极大地刺激了大气中的 H ₂氧化。总之，这些发现强调了 H ₂是一种重要的、迄今为止被忽视的能源，支持沙漠土壤中的细菌群落。 然而，与我们之前的假设相反，在此类生态系统中，H ₂氧化与光合作用同时发生，而不是交替发生，甚至可能由一些光合自养生物介导。