A distinct and active bacterial community in cold oxygenated fluids circulating beneath the western flank of the Mid-Atlantic ridge

Abstract

The rock-hosted, oceanic crustal aquifer is one of the largest ecosystems on Earth, yet little is known about its indigenous microorganisms. Here we provide the first phylogenetic and functional description of an active microbial community residing in the cold oxic crustal aquifer. Using subseafloor observatories, we recovered crustal fluids and found that the geochemical composition is similar to bottom seawater, as are cell abundances. However, based on relative abundances and functional potential of key bacterial groups, the crustal fluid microbial community is heterogeneous and markedly distinct from seawater. Potential rates of autotrophy and heterotrophy in the crust exceeded those of seawater, especially at elevated temperatures (25 °C) and deeper in the crust. Together, these results reveal an active, distinct, and diverse bacterial community engaged in both heterotrophy and autotrophy in the oxygenated crustal aquifer, providing key insight into the role of microbial communities in the ubiquitous cold dark subseafloor biosphere.

Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust

“…Discrete fluid samples were collected from umbilicals 0.5, 2.5, and 6 years after Holes U1382A and U1383C were deployed (Meyer et al, ; Tully et al, : this work). During this 6‐year period, the composition of the fluids changed (Table ).…”

“…Also Hole U1383B was not sealed prior to fluid sampling in 2012, thus the high DO concentrations in fluids from Hole U1383C could result, in part, from continued influx of bottom seawater after drilling operations ceased. Thus, microbial data from 2012 represent a mixture of community sources (bottom and surface (from drilling) seawater and formation fluids) (Meyer et al, ; Tully et al, ; Walter et al, ) and should be viewed in this context. Comparison of DO data from 2014 and 2017 suggest that the formation fluid may have continued to rebound from drilling disturbances; however, other solute data suggest that the boreholes had chemically rebounded by 2014.…”

In situ Electrochemical Studies of the Terrestrial Deep Subsurface Biosphere at the Sanford Underground Research Facility, South Dakota, USA

“…EET can be electrochemically mimicked on electrode surfaces that function as surrogate electron acceptors (anodes) or donors (cathodes) to support microbial metabolism, depending on the poised potentials of these electrodes (Bond and Lovley, 2003;Gregory et al, 2004;Ross et al, 2011;Carmona-Martínez et al, 2013;Rowe et al, 2017a;Hirose et al, 2018). As a result, electrochemical enrichments have been applied to microbial samples from a variety of environments (Bond et al, 2002;Tender et al, 2002;Holmes et al, 2004;Kim et al, 2004;Rabaey and Verstraete, 2005;Reimers et al, 2006;White et al, 2009;Bond, 2010;Meyer et al, 2016). When combined with surveys of microbial community structure, these electrochemical techniques greatly expanded our understanding of the phylogenetic diversity of microbes capable of colonizing electrodes and led to the isolation of novel microorganisms capable of EET to anodes (Wrighton et al, 2008;Xing et al, 2008;Fedorovich et al, 2009;Badalamenti et al, 2016;Jangir et al, 2016;Kawaichi et al, 2018).…”

Resident bacterial populations mediating biogeochemical dynamics in a Uranium roll front deposit

“…Genera like Flavobacterium, Pseudomonas and Aquabacterium, the dominant genera here, occur more frequently and abundantly in this type of water samples. According to the literature, these genera have a widespread occurrence in water environments, where they decompose organic matter[43,44]. On the other hand, high concentrations of nitrate, sulphate, and Fe were found in this section of the aquifer.…”