Abstract
Microorganisms influence biogeochemical cycles from the surface down to the depths of the continental rocks and oceanic basaltic crust. Due to the poor recovery of microbial isolates from the deep subsurface, the influence of physical environmental parameters, such as pressure and temperature, on the physiology and metabolic potential of subsurface inhabitants is not well constrained. We evaluated Fe(III) reduction rates (FeRRs) and viability, measured as colony-forming ability, of the deep-sea piezophilic bacterium Shewanella profunda LT13a over a range of pressures (0–125 MPa) and temperatures (4–37∘C) that included the in situ habitat of the bacterium isolated from deep-sea sediments at 4500 m depth below sea level. S. profunda LT13a was active at all temperatures investigated and at pressures up to 120 MPa at 30∘C, suggesting that it is well adapted to deep-sea and deep sedimentary environments. Average initial cellular FeRRs only slightly decreased with increasing pressure until activity stopped, suggesting that the respiratory chain was not immediately affected upon the application of pressure. We hypothesize that, as pressure increases, the increased energy demand for cell maintenance is not fulfilled, thus leading to a decrease in viability. This study opens up perspectives about energy requirements of cells in the deep subsurface.
Highlights
Less than 1% of microorganisms of the environment have been isolated in pure cultures (Amann et al, 1995)
We investigated the effects of temperature on iron reduction by strain LT13a at 4, 10, 20, 30, and 37◦C at atmospheric pressure (Figure 1)
CELL DENSITY AFFECTS P RANGES OF ACTIVITY AND SURVIVAL At ambient pressure, Fe(III) reduction rates (FeRRs) increased with increasing initial colony-forming unit (CFU) concentration (Figure 2), as seen in other studies with S. alga BrY (Roden and Zachara, 1996) and Geobacter sulfurreducens
Summary
Less than 1% of microorganisms of the environment have been isolated in pure cultures (Amann et al, 1995). Pressure is a unique parameter of deep subsurface environments and increases at a rate of 10, 15, and 28 MPa km−1 in the water column, sediments and continental, and oceanic rocks, respectively. The comparison between piezophilic and piezo-sensitive microorganisms has revealed physiological and molecular adaptations to life under pressure (Simonato et al, 2006; Lauro and Bartlett, 2007), such as a unique membrane composition of piezophilic bacteria (DeLong and Yayanos, 1985), an increase in certain amino acids in proteins of piezophilic archaea (Di Giulio, 2005) or pressure-regulated gene expression in some deep-sea bacteria (Bartlett et al, 1995; Nakasone et al, 1998)
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