The Integrated Ocean Drilling Program (IODP) Hole 1301A on the eastern flank of Juan de Fuca Ridge was used in the first long-term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole.Three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks.Following recovery of the colonization systems, we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples.We also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine R2A medium and identified isolates by partial 16S or 18S rDNA sequencing.We found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron.Fe(II)-rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles, as well as the only culturable organotrophic thermophiles.These results suggest that olivine (a common igneous mineral) in seawater-recharged ocean crust is capable of supporting microbial communities, that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes, and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust.
Specific surface area (SSA) was measured on 13 samples of basalt recovered from Integrated Ocean Drilling Program Expedition 301 Hole U1301B drilled on the east flank of Juan de Fuca Ridge.SSA ranged from 0.3 to 52 m 2 /g.SSA is positively correlated with porosity and inversely correlated with bulk density and P-wave velocity.Excluding two breccia samples (with SSAs of 29 and 52 m 2 /g), the average SSA was 2.3 m 2 /g.Data report: specific surface area and physical properties of subsurface basalt samples from the east flank of Juan de Fuca Ridge 1
These first measurements of specific surface area (SSA) of bulk samples of subsurface marine basalts were undertaken to determine the potential area available for microbial colonization. SSA ranged from 0.3 to 52 m 2 /g of basalt with the lowest value coming from pillow basalt and the highest value from breccia. The average for massive and pillow basalts combined was 2.3 m 2 /g. The total specific surface area of the extrusive volcanic rocks of the ocean crust is estimated to be 10 24 m 2 . This surface area could provide attachment for up to 10 34 cells if cell density is the same as that of experimentally colonized basalt surfaces. Independent measures and calculations of biomass in basalts suggest that cell densities on surfaces are only 10 −4 times those in laboratory experiments and, therefore, the surface area of basalt does not limit microbial biomass in the igneous ocean crust.
Two designs of benthic microbial fuel cell (BMFC) were deployed at cold seeps in Monterey Canyon, CA, unattended for between 68 and 162 days. One design had a cylindrical solid graphite anode buried vertically in sediment, and the other had a carbon fiber brush anode semi-enclosed in a chamber above the sediment–water interface. Each chamber included two check valves to allow fluid flow from the sediment into the chamber. On average, power outputs were 0.2 mW (32 mW m−2 normalized to cross sectional area) from the solid anode BMFC and from 11 to 56 mW (27–140 mW m−2) during three deployments of the chambered design. The range in power produced with the chambered BMFC was due to different valve styles, which appear to have permitted different rates of chemical seepage from the sediments into the anode chamber. Valves with the lowest breaking pressure led to the highest power production and presumably the highest inputs of electron donors. The increase in power coincided with a significant change in the microbial community associated with the anode from being dominated by epsilonproteobacteria to a more diverse community with representatives from deltaproteobacteria, epsilonproteobacteria, firmicutes, and flavobacterium/cytophaga/bacterioides (FCB). The highest levels of power delivered by the chambered BMFC would meet the energy requirements of many oceanographic sensors marketed today. In addition, these BMFCs did not exhibit signs of electrochemical passivation or progressive substrate depletion as is often observed with buried anodes.
ABSTRACT There is widespread interest in developing methods to investigate in situ microbial activity in subsurface environments. Novel experiments based on single borehole push–pull methods were conducted to measure in situ microbial activity at the Äspö Hard Rock Laboratory (HRL). Microbial nitrate reduction and lactate consumption were measured at in situ conditions at a depth of 450 m in the HRL tunnel. A circulation system was used to circulate ground water from the aquifer through pressure‐maintaining flow cells containing coupons for biofilm growth. The system allows microbial investigations at in situ pressure, temperature and chemistry. Four experiments were conducted in which a combination of a conservative tracer, nitrate and lactate was injected into the circulation system. Rate of nitrate utilization was 5 µ m h −1 without lactate and 13 µ m h −1 with lactate. Lactate consumption increased from 30 to 50 µ m h −1 with the addition of an exogenous electron acceptor (nitrate). Attached and unattached cells were enumerated using epifluorescence microscopy to calculate cell‐specific rates of activity. The biofilm had an average cell density of 1 × 10 6 cells cm −2 and there was an average of 6 × 10 5 unattached cells mL −1 in circulation. Cell‐specific rates of lactate consumption were higher than previously reported using radiotracer methods in similar environments. The differences highlight the importance of conducting microbial investigations at in situ conditions. The results demonstrate that an indigenous community of microbes survives at a depth of 450 m in the Fennoscandian shield aquifer with the potential to oxidize simple organic molecules such as lactate.
