The Iheya North Hydrothermal Field in the Okinawa Backarc Basin represents an ideal environment in which to investigate the biotic temperature fringe of microbial life at depth because of its subsurface hydrothermal activity within its continental margin-type sediment profile. Geographically, the Okinawa Backarc Basin is situated along a continental margin, which is a sediment profile type commonly sampled and studied across the seafloor (e.g. Peru Margin, Costa Rica Margin, Cascadia Margin). The hydrothermal network within the subsurface here supplies an additional temperature obstacle to microbial life existing in the sediments. In particular, the sediment profile at Site C0014 exhibits a transition from hemipelagic ooze with pumiceous volcaniclastic sediments and low temperature (4°C) to a hydrothermally altered sequence of clays within the top ~10 mbsf of sediment. Temperature measurements indicate a gradient of approximately 3°C/m, which is roughly an order of magnitude greater than continental margin sites (e.g. Cascadia Margin, IODP 311 and Costa Rica Margin, IODP 344), but is more gradual than intense, centimeter-scale gradients from other hot, surface sediments. We have focused on the application of culture-independent, molecular methods to understand taxonomic and functional characteristics through this hydrothermal gradient. Confidence in DNA recovery suggests a microbial biosphere extent of approximately 15 mbsf (55°C).

Results from both 16S rRNA gene surveys and metagenomics analyses suggest a temperature-dependent stratigraphy of taxonomic and functional adaptations between the shallowest and deepest sample horizons. Cosmopolitan marine subsurface bacterial and archaeal taxa are present throughout the top 10 mbsf, whereas, hyperthermophilic heterotrophic as well as thermophilic anaerobic methanotrophic archaea appear in varying local abundances in deeper, hydrothermal clay horizons. “An In-Depth analysis of the subvent biosphere within Okinawa Backarc Basin (IODP 331, Iheya North Hydrothermal Field) sediments” encompasses datasets funded through C-DEBI to investigate the microbial communities in IODP 331 Iheya North Hydrothermal Field sediments. Site C0014 at this field site is 500 m away from the active vent and experiences a 3C/m temperature gradient with depth. In the research grant “Investigating the active microbial populations in near hydrothermal vent sediments” and the Research Exchange grant “Learning new RNA extraction techniques”, we used an RNA-based approach to explore the active microbial community. Upon analysis, the RNA dataset does not appear to reflect the same information as the phylogenetic signals coming from both the 16S rRNA gene as well as the metagenomes. The data indicate significant background noise from the RNA extraction process rather than from an indigenous representation of the subsurface biosphere.

The graduate fellowship “An in-depth analysis of the subvent biosphere within the Okinawa backarc basin Iheya North hydrothermal field” provided an opportunity to bring together metagenomic, 16S rRNA gene amplicon (DNA), and 16S rRNA amplicon datasets from IODP 331 Iheya North Hydrothermal Field sediments to understand the biogeography of this subvent biosphere.

For more information, refer to the following C-DEBI grants/projects.
An in-depth analysis of the subvent biosphere within the Okinawa backarc basin Iheya North hydrothermal field:
https://www.darkenergybiosphere.org/award/an-in-depth-analysis-of-the-subvent-biosphere-within-the-okinawa-backarc-basin-iheya-north-hydrothermal-field/

Investigating the active microbial populations in near hydrothermal vent sediments: https://www.darkenergybiosphere.org/award/investigating-the-active-microbial-populations-in-near-hydrothermal-vent-sediments/

Learn new RNA extraction techniques: https://www.darkenergybiosphere.org/award/learn-new-rna-extraction-techniques/