Microbial Mat Boundaries between Chemolithotrophs and Phototrophs in Geothermal Hot Spring Effluents |
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Authors: | Kenji Kato Takeshi Kobayashi Hiroyuki Yamamoto Takkou Nakagawa Yonosuke Maki Toshihiro Hoaki |
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Institution: | 1. Institute of Geoscience, Faculty of Science, Shizuoka University , Shizuoka, Japan;2. Laboratory of Environmental Science and Microbiology, Graduate School of Pharmaceutical Sciences, Osaka University , Suita, Japan;3. Japan Marine Science and Technology Center , Yokosuka, Japan;4. Department of Biology, Faculty of Science, Tokyo Metropolitan University , Hachio-ji, Japan;5. Laboratory of Biology, Faculty of Humanities and Social Sciences, Iwate University , Morioka, Japan;6. Biotechnology Section, Taisei Corporation Research Center , Yokohama, Kanagawa, Japan |
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Abstract: | Among the various microbial mats that develop in geothermal hot springs in solfataric fields, colorless sulfur-turf (ST)—macroscopic white bundles consisting of large sickle-shaped bacteria belonging to Aquificales and elemental sulfur particles–develops in a limited environment of geothermal effluent containing hydrogen sulfide with neutral pH and low in oxygen. Photosynthetic cyanobacterial mat (CY) often grow just downstream of chemolithotrophic ST, or they coexist with ST where the temperature is slightly lower. Knowledge of the environmental regimes of these microbial mats will lead to better understanding of the distribution of thermophilic microorganisms on the Earth and provide clues about evolutionary processes in the microbial ecosystems of the Precambrian era. We studied the environmental parameters of the boundary zone and examined the distribution of these types of mats and measured the in situ growth rates of the microorganisms composing them. In situ examination revealed that temperature and Eh constrain the development of the microbial mats. At the boundary between ST and CY, temperature and Eh ranged between 51.1°C and 63.2°C and between ?112 mV and ?25 mV, respectively. These environmental parameters were not significantly different among Japanese, Yellowstone (North American), and Icelandic hot spring effluents with genetically similar thermal sulfur oxidizers. Sickle-shaped bacteria rarely coexist with cyanobacteria, although they can potentially grow in some CY environments. This suggests that the boundary between ST and CY might be partly determined by exclusive ecological competition. |
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Keywords: | boundary chemolithotroph cyanobacterial mat hot spring oxidation–reduction potential phototroph sulfurturf temperature gradient |
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