Bacterial Variability within an Iron-Silica-Manganese-rich Hydrothermal Mound Located Off-axis at the Cleft Segment, Juan de Fuca Ridge

Abstract Terminal-restriction fragment length polymorphisms (T-RFLPs) and traditional clone library analysis were used to identify and assess the spatial variability of microbial communities within an active diffusely venting hydrothermal mound found 4 km off-axis at the Cleft Segment, Juan de Fuca Ridge. T-RFLP fingerprints were generated from three subsamples taken from different depths of a sediment core. The top and center subsamples were dominated by phylotypes clustering with the proposed ζ -Proteobacteria. The bottom of the core was dominated by a phylotype clustering in the Nitrospina group within the δ -Proteobacteria. Cluster analysis of T-RFLP fingerprints from the center of the core shows a similar community structure with those from iron-dominated microbial mat communities collected from NW Eifuku Seamount in the Mariana Island Arc and from Loihi Seamount, Hawaii. Our study demonstrates that off-axis diffuse hydrothermal activity generates microbial communities that can potentially affect their habitat through the differential precipitation of Fe-, Si-, and Mn-rich deposits. Keywords: biogeochemical cyclingbiomineralizationcommunity structureiron-oxidizing bacteria We would like to thank the captain and crew of the of the R/V Western Flyer and the pilots of the ROV Tiburon for all their efforts during the collection of these samples. Funds from the Lucile and David Packard Foundation provided to MBARI supported the oceanographic expedition described in this study. This research was also supported in part by NOAA's Office of Ocean Exploration, the Office of Research and Sponsored Programs at Western Washington University and by National Science Foundation awards MCB-0348734 (to CLM) and GEBSN0056A (to RED).