Molecular evidence demonstrating the basidiomycetous fungus Cryptococcus curvatus is the dominant microbial eukaryote in sediment at the Kuroshima Knoll methane seep
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The Kuroshima Knoll, located in the southern Ryukyu Arc, is known to actively bubble with gas containing methane and hydrogen sulfide from numerous fissures in the large carbonate pavement. Although ecological studies regarding macrobenthos and bacteria from Kuroshima Knoll have been intensively conducted, the community structure and ecological importance of microbial eukaryotes (protists) have not yet been investigated. In the present study, we directly extracted DNA from sediment of the Kuroshima Knoll at a depth of 640 m and constructed genetic libraries of PCR-amplified eukaryotic small-subunit ribosomal DNA (SSU rDNA). Although the SSU rDNA sequences of several types of benthic foraminifers were retrieved from the surface of the sediment, all other sequences (just below the sediment surface to approximately 9 cm below sediment surface) were derived from the basidiomycetous yeast Cryptococcus curvatus. Furthermore, sequences of the internal transcribed spacer of rDNA (ITS-rDNA) retrieved from the same sediment were identical to that of C. curvatus originating from terrestrial habitats. The diversity of microbial eukaryotes in the Kuroshima Knoll sediment seems to be extremely low and significantly different from that of other marine environments previously reported.
KeywordsDeep-sea Eukaryotes Foraminifers Fungus ITS-rDNA Methane seep SSU rDNA
We thank Dr. M. Nishijima (NCIMB Japan) for useful information on yeast literature; Mr. M. Kawato (JAMSTEC) for technical assistance; the captain and crew of the R/V Natsushima and the commander, pilots and operation team of the ROV Hyper-Dolphin for dedicated efforts. This work was performed as part of the project ‘Study for Understanding of Function and Structure of the Marine Ecosystems in the Earth Systems’ conducted at JAMSTEC, and was supported in part by grants from the Japan Society for the Promotion of Science (No. 17770077 to K. Takishita).
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