Photosynthetic bacteria are abundant in alkaline, terrestrial hot springs and there is a long history of research on phototrophs in Yellowstone National Park (YNP). Hot springs provide a framework to examine the ecophysiology of phototrophs in situ because they provide natural gradients of geochemistry, pH and temperature. Phototrophs within the Cyanobacteria and Chloroflexi groups are frequently observed in alkaline hot springs. Decades of research has determined that temperature constrains Cyanobacteria in alkaline hot springs, but factors that constrain the distribution of phototrophic Chloroflexi remain unresolved. Using a combination of 16S rRNA gene sequencing and photoassimilation microcosms, we tested the hypothesis that temperature would constrain the activity and composition of phototrophic Cyanobacteria and Chloroflexi. We expected diversity and rates of photoassimilation to decrease with increasing temperature. We report 16S rRNA amplicon sequencing along with carbon isotope signatures and photoassimilation from 45 to 72°C in two alkaline hot springs. We find that Roseiflexus, Chloroflexus (Chloroflexi) and Leptococcus (Cyanobacteria) operational taxonomic units (OTUs) have distinct distributions with temperature. This distribution suggests that, like phototrophic Cyanobacteria, temperature selects for specific phototrophic Chloroflexi taxa. The richness of phototrophic Cyanobacteria decreased with increasing temperature along with a decrease in oxygenic photosynthesis, whereas Chloroflexi richness and rates of anoxygenic photosynthesis did not decrease with increasing temperature, even at temperatures approaching the upper limit of photosynthesis (~72–73°C). Our carbon isotopic data suggest an increasing prevalence of the 3‐hydroxypropionate pathway with decreasing temperature coincident with photoautotrophic Chloroflexi. Together these results indicate temperature plays a role in defining the niche space of phototrophic Chloroflexi (as has been observed for Cyanobacteria), but other factors such as morphology, geochemistry, or metabolic diversity of Chloroflexi, in addition to temperature, could determine the niche space of this highly versatile group.

中文翻译：

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温度影响黄石国家公园两个碱性温泉中光养绿藻和蓝藻的群落结构和功能。


碱性地热温泉中含有丰富的光合细菌，黄石国家公园 (YNP) 对光合细菌的研究也有着悠久的历史。温泉提供了一个框架来检查光养生物的生态生理学，因为它们提供了地球化学、pH 值和温度的自然梯度。在碱性温泉中经常观察到蓝藻菌和绿屈菌群中的光养生物。数十年的研究已经确定，温度限制了碱性温泉中的蓝细菌，但限制光养绿屈菌分布的因素仍未解决。通过结合 16S rRNA 基因测序和光同化微观世界，我们测试了温度会限制光养蓝细菌和 Chloroflexi 的活性和组成的假设。我们预计多样性和光同化率会随着温度的升高而降低。我们报告了两个碱性温泉中 45 至 72°C 的 16S rRNA 扩增子测序以及碳同位素特征和光同化。我们发现Roseiflexus 、 Chloroflexus (Chloroflexi) 和Leptococcus (Cyanobacteria) 操作分类单位 (OTU) 随温度具有不同的分布。这种分布表明，与光养蓝细菌一样，温度选择特定的光养绿柔菌类群。光养蓝藻的丰富度随着温度的升高而降低，同时产氧光合作用的减少，而绿柔菌的丰富度和无氧光合作用的速率并不随着温度的升高而降低，即使在接近光合作用上限（~72-73°C）的温度下也是如此。 我们的碳同位素数据表明，随着温度的降低，3-羟基丙酸途径的患病率不断增加，这与光合自养 Chloroflexi 一致。这些结果共同表明，温度在定义光养绿柔菌的生态位空间中发挥着重要作用（正如在蓝细菌中观察到的那样），但除了温度之外，其他因素，如绿柔菌的形态、地球化学或代谢多样性，也可以决定生态位空间。这个高度多才多艺的群体。