Project: Iron-oxidizing Bacteria from the Okinawa Trough Deep Subsurface Biosphere

Description from NSF award abstract:
Communities of Fe-oxidizing Bacteria (FeOB) are common at sites of hydrothermal venting and are known to form complex communities in microbial mats, hydrothermal sediments, oceanic crustal basalts and borehole fluids (among others) that are iron-rich and low in oxygen. Studies from sites around the Pacific Ocean have found the Zetaproteobacteria to be ubiquitous members of these FeOB communities. Previously, borehole fluids from the Southern Mariana Backarc have been shown to support several novel and distinct lineages of endemic Zetaproteobacteria. Sampling from the deep subsurface at the Iheya North hydrothermal field (IODP Expedition 331) explores this deep subsurface FeOB biodiversity and has resulted in multiple enrichments using both microaerophilic and anaerobic culturing conditions. Zetaproteobacteria have been detected at levels up to 13% of the total bacterial community from these subsurface core samples. This project expands post-cruise analyses to focus on assessing these FeOB subsurface communities using a combined single cell genomics, community-level metagenomics and a FeOB directed cultivation approach. This approach will allow insights into the exclusive physiology and metabolism of these Zetaproteobacteria thereby demonstrating key features as to how they survive, compete and grow within these complex subsurface microbial communities. A comparative analysis (from an evolutionary standpoint) to determine the unique differences between subsurface Zetaproteobacteria and those living above the seafloor surface is an integral part of this effort.

A better understanding of Zetaproteobacteria is of central interest to scientists interested in areas of earth science and oceanography because they illustrate how microbes can influence geochemical cycling and mineral deposition. Furthermore, morphological structures similar to those produced by Zetaproteobacteria can still be identified 100's of millions (and possibly billions) of years back in the rock record, making them of paleontological (and potentially of exobiological) interest. As knowledge of extant populations grows, it is possible they will also help to inform us of environmental change in past Earth history. From a practical standpoint, these organisms might be thought of as 'micro-machines', spinning out threads of iron oxyhydroxide that coalesce in unknown ways. These oxides are known to be highly reactive with a range of other metals, organic compounds, and nutrients, thus impacting many other biogeochemical cycles. In particular, this study allows the opportunity to compare and contrast a known monophyletic class of Proteobacteria, to study the differences between subsurface and supersurface lineages of Zetaproteobacteria, thereby yielding fundamental clues into microbial biogeography. A wealth of educational outreach opportunities will be made possible by this work, including graduate education, research experiences for undergraduates, and teacher training.

Related Publications:

Fullerton, H. and C. L. Moyer. 2016. Comparative single-cell genomics of Chloroflexi from the Okinawa Trough deep subsurface biosphere. Appl. Environ. Microbiol. 82:3000-3008. doi: 10.1128/AEM.00624-16

Takai, K., Mottl, M. J., Nielsen, S. H. H., and the IODP Expedition 331 Scientists: IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough, Sci. Dril., 13, 19-27, doi:10.5194/sd-13-19-2012, 2012.

Yanagawa K, Nunoura T, McAllister SM, Hirai M, Breuker A, Brandt L, House CH, Moyer CL, Birrien J-L, Aoike K, Sunamura M, Urabe T, Mottl MJ and Takai K (2013) The first microbiological contamination assessment by deep-sea drilling and coring by the D/V Chikyu at the Iheya North hydrothermal field in the Mid-Okinawa Trough (IODP Expedition 331). Front. Microbiol. 4:327. doi:10.3389/fmicb.2013.00327.