Deep Subsurface Biosphere of a Hydrothermal Vent Field in the Manus Basin of the Western Pacific.

Abstract

Occurrence and distribution of microorganisms in the subsurface of deep-sea hydrothermal ventssub-ventswere investigated using sub-vent rock samplescores, approximately 6.5 cm in diameter collected by the Ocean Drilling Program ODP . The central parts of the cores subcores, approximately 1.5 cm in diameter were extracted in an anaerobic chamber. The degree of contamination by drilling fluidsurface seawater in ODPwas tested using perfluorocarbonPFCtracers. The test showed that PFC-traced contamination was limited to core surfaces and was not detected in subcores. Therefore, subcores were used in microbiological analyses for direct counts, adenosine 5-triphoshateATPmeasurements, thermophilic incubations, and 16S ribosomal RNA gene 16S rDNA sequences. Microbial cells in the subcores were observed from depths shallower than 97.9 meters below the seafloor mbsfby 46 -diamidino-2-phenylindoleDAPI -epifluorescence microscopy. Similarly, ATP was detected only from depths shallower than 44.8 mbsf by the luciferin-luciferase method. Portions of subcores from various depths, 9.7-301.5 mbsf, were directly incubated anaerobically with a heterotrophic medium at temperatures of 60 and 90 . After two weeks, an increase in cell numbers was observed for 60 -cultures from 59.8 99.4 mbsf samples, and for 90 -cultures from 69.1-128.9 mbsf samples. The 16S rDNA sequences suggest that microorganisms from the 60 -and 90 -cultures are closely related to the thermophilic species belonging to the genera Geobacillus and Deinococcus, respectively. These results indicate 1 existence of microbial habitats in the sub-vent region of subseafloor, and 2 habitat segregation of thermophilic bacteria over the sub-vent thermal gradient.