Abstract
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.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 503-513 |
| Number of pages | 11 |
| Journal | Environmental microbiology reports |
| Volume | 12 |
| Issue number | 5 |
| DOIs | |
| State | Published - Oct 1 2020 |
Bibliographical note
Funding Information:T. L. H. conducts research in Yellowstone National Park under research permit YELL-2018-SCI-7020 issued by the Yellowstone Research Permit Office (to T. L. H. and Jeff Havig) and reviewed annually. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper. We are grateful to the entire staff of the Yellowstone Research Permit Office for facilitating the permitting process to perform research in YNP. Special thanks to Annie Carlson and Erik Oberg in the Yellowstone Research Permit Office. We thank J. Havig, L. Brengman, C. Grettenberger, L. Seyler, and J. Kuether for technical assistance in the field and A. Borowski and K. Quinn for assistance processing samples in the lab.
Publisher Copyright:
© 2020 The Authors. Environmental Microbiology Reports published by Society for Applied Microbiology and John Wiley & Sons Ltd.