High-pressure biotopes comprise cold deep-sea environments, hydrothermal vents, and deep subsurface or deep-sea sediments. The latter are less studied, due to the technical difficulties to sample at great depths without contamination. Nevertheless, microbial sulfate reduction and methanogenesis have been found to be spatially distributed in deep deep-sea sediments (1), and sulfate reduction has been shown to be actually more efficient under high hydrostatic pressure (HHP) in some sediments (2). Sulfate-reducing bacteria obtained from the Japan Sea are characterized by an increased sulfide production under pressure (3,4). Unfortunately, investigations of microbial metabolic activity as a function of pressure are extremely scarce due to the experimental difficulty of such measurements at high hydrostatic pressure. We were able to measure the reduction of selenite Se(IV) by Shewanella oneidensis MR-1 as a function of pressure, to 150 MPa using two different high-pressure reactors that allow in situ X-ray spectroscopy measurements on a synchrotron source. A first series of measurements was carried out in a low-pressure Diamond Anvil Cell (DAC) of our own design (5) at ID22 beamline at ESRF (European Synchrotron Radiation Facility); a second one was performed in an autoclave (6) at the BM30B beamline at ESRF. Selenite reduction by strain MR-17 was monitored from ambient pressure to 150 MPa over 25 hours at 30 deg C by XANES spectroscopy (X-ray Analysis of Near Edge Structure). Spectra were recorded hourly in order to quantify the evolution of the oxidation state of selenium with time. Stationary-phase bacteria were inoculated at a high concentration into fresh growth medium containing 5 or 10 M of sodium selenite and 20 mM sodium lactate. Kinetic parameters of the Se (IV) reduction by Shewanella oneidensis strain MR-1 could be extracted from the data, as a function of pressure. They show 1) that the rate constant k of the reaction is decreased by a half at high pressure, and 2) that the yield of the reaction decreases linearly as a function of pressure. From the present study, we can infer the maximum pressure of the metabolism of Se by Shewanella oneidensis strain MR-1 at ca. 160 MPa. The present results indicate that even piezosensitive bacteria can harbor a significant amount of metabolic activity at pressure conditions that are relevant for subsurface geochemical cycles. Moreover, one can hypothetize the same implications in the cycles of more abundant elements, like Fe or Mn. 1 S. D'Hondt, et al., Science 306, 2216-2221 (2004). 2 J. Kallmeyer and A. Boetius, Appl Environ Microbiol 70, 1231-1233 (2004). 3 S. Bale, K. et al., Int J Syst Bacteriol 47, 515-521 (1997). 4 R. J. Parkes, et al. J Microbiol Methods 23, 235-249 (1995). 5 I. Daniel, et al. in prep (2007). 6 D. Testemale, et al. Rev Sci Instrum 76, 043905 (2005). 7 C. R. Myers and K. H. Nealson, J Bacteriol 172, 6232-6238 (1990).
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0448 Geomicrobiology;
- 0456 Life in extreme environments