Temperature and Redox Effect on Mineral Colonization in Juan de Fuca Ridge Flank Subsurface Crustal Fluids.

Jean-Paul M Baquiran,Samuel Hulme,Beth N Orcutt,Gustavo A Ramírez,Katrina J Edwards,Brandy M Toner,Charles G Wheat,Amanda G Haddad

doi:10.3389/fmicb.2016.00396

Abstract

To examine microbe-mineral interactions in subsurface oceanic crust, we evaluated microbial colonization on crustal minerals that were incubated in borehole fluids for 1 year at the seafloor wellhead of a crustal borehole observatory (IODP Hole U1301A, Juan de Fuca Ridge flank) as compared to an experiment that was not exposed to subsurface crustal fluids (at nearby IODP Hole U1301B). In comparison to previous studies at these same sites, this approach allowed assessment of the effects of temperature, fluid chemistry, and/or mineralogy on colonization patterns of different mineral substrates, and an opportunity to verify the approach of deploying colonization experiments at an observatory wellhead at the seafloor instead of within the borehole. The Hole U1301B deployment did not have biofilm growth, based on microscopy and DNA extraction, thereby confirming the integrity of the colonization design against bottom seawater intrusion. In contrast, the Hole U1301A deployment supported biofilms dominated by Epsilonproteobacteria (43.5% of 370 16S rRNA gene clone sequences) and Gammaproteobacteria (29.3%). Sequence analysis revealed overlap in microbial communities between different minerals incubated at the Hole U1301A wellhead, indicating that mineralogy did not separate biofilm structure within the 1-year colonization experiment. Differences in the Hole U1301A wellhead biofilm community composition relative to previous studies from within the borehole using similar mineral substrates suggest that temperature and the diffusion of dissolved oxygen through plastic components influenced the mineral colonization experiments positioned at the wellhead. This highlights the capacity of low abundance crustal fluid taxa to rapidly establish communities on diverse mineral substrates under changing environmental conditions such as from temperature and oxygen.

Highlights

The deep subsurface biosphere represents a vast and relatively unknown environment
flow-through osmotic colonization systems (FLOCS) chambers were assembled onsite, with one FLOCS chamber consisting of cassettes containing glass wool with an olivine-rich basalt from the Loihi Seamount (GW + basalt in Table 1) in Sleeve 2; cassettes of pyrite (FeS2) and of massive basalt previously collected from the Juan de Fuca Ridge flank subsurface at Integrated Ocean Drilling Program (IODP) Hole U1301B (“Basalt” in Table 1) in Sleeves 5 and 1; and hematite (Fe2O3) and goethite [FeO(OH)] in Sleeves 5 and 1, respectively (Figure 2)
In the quest to study microbial life supported by the deep crustal biosphere—a major focus of the international ocean drilling program (Iodp 2003-2013 Initial Science Plan, 2001)— this experiment set out to examine the utility of deploying mineral colonization experiments at the wellheads of crustal subsurface borehole observatories (i.e., Circulation Obviation Retrofit Kit (CORK)) as an alternative to downhole deployments (Figure 2)

Summary

Introduction

The deep subsurface biosphere represents a vast and relatively unknown environment. While this deep biosphere is estimated to comprise a significant fraction of the Earth’s total biomass (Whitman et al, 1998; Kallmeyer et al, 2012), most investigations have focused on the marine sedimentary realm (Parkes et al, 2000; D’hondt et al, 2004; Biddle et al, 2006; Jørgensen and Boetius, 2007; Teske and Sørensen, 2008; Lever et al, 2010). Results indicate that the deep subsurface rock-hosted biosphere is different from overlying sediment in terms of the abundance and distribution of biological taxa (Thorseth et al, 2001; Cowen et al, 2003; Lysnes et al, 2004; Mason et al, 2010; Edwards et al, 2011a; Orcutt et al, 2011a; Jungbluth et al, 2013) Fluids within this highly porous and permeable crust are exchanged via advection with the overlying oceans, resulting in a flux of chemicals to and from the oceans that are significant to global geochemical budgets for some elements (Elderfield and Schultz, 1996; Wheat et al, 2003b). Such chemical exchange reactions are the foundation for chemolithotrophic microbial life (Bach and Edwards, 2003); factors controlling substrate colonization, bioalteration, microbial proliferation, and ecosystem establishment in crustal aquifer environments are largely unknown (Edwards et al, 2012b)

Methods

Results

Discussion

Conclusion