Microbial Diversity in Acidic High-Temperature Steam Vents
Fumaroles represent one of the most abundant and understudied geothermal features on Earth. Recent discoveries of microorganisms transported in steam from the subsurface have increased interest in these extreme habitats. Isolation of environmental DNA from high-temperature low-pH steam deposits poses considerable challenges and has foiled many previous studies. We examined samples of steam deposits collected from steam caves/vents in three national parks, Hawaii Volcanoes National Park, Yellowstone National Park, and Lassen Volcanic National Park, and other more remote international sites for their chemical constituents and microbial populations. DNA culture-independent analysis of condensed steam generated from the subsurface showed that it carried halophilic organisms (Archaea), despite a paucity of dissolved ions. Several of these halophiles were also cultivated from the Hawaiian steam deposit samples. As found in previous studies, DNA isolation from deposits in direct contact with subsurface steam proved to be refractory to isolation in many of the cave/vent deposit samples. However, our modifications of existing DNA extraction methods yielded DNA in half of the samples, providing the first evidence of Archaea in steam deposit habitats. BLAST analysis of the resulting 16S rRNA gene sequences showed that sulfur steam caves and vents were inhabited by Sulfolobus and Acidianus. Nonsulfur cave inhabitants were represented by novel Crenarchaeota, and Hawaiian samples contained novel lineages related to ammonia-oxidizing Archaea in the newly proposed Thaumarchaeota. The 50 % of samples that proved to be refractory to DNA isolation eventually yielded cultures that were shown to be related to Sulfolobus or unknown Archaea. Recent culture-independent analysis of bacterial diversity in these habitats found them to be a complex and heterogeneous habitat composed of many extremophile lineages. These results show fumaroles to be a rich source of microorganisms that represent new and unknown microbes.
KeywordsThin Filament amoA Gene Condensed Steam Flowing Spring Cave Deposit
The authors acknowledge the assistance of Dr. Steve Barlow and use of equipment at the San Diego State University Electron Microscopy Facility acquired by NSF Instrumentation grant DBI-0959908. We thank the National Park Service at Yellowstone National Park, Lassen Volcanic National Park, and Hawaii Volcanoes National Park for assistance and allowing our collections. We also thank Caryl McHarney, Benno Spingler, Xzayla Xibiti, and our graduate students who assisted or contributed ideas during the design of the steam collector. We thank Lisa Thurn for chemistry, and Courtney Benson, Wendy Gutierrez, Ann McAfee, and Harmony Saunders for the microbial culture. The generous contributions of Schering-Plough Biopharma are gratefully acknowledged.
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