skip to main content


Title: The effect of O 2 and pressure on thiosulfate oxidation by Thiomicrospira thermophila
Abstract

Microbial sulfur cycling in marine sediments often occurs in environments characterized by transient chemical gradients that affect both the availability of nutrients and the activity of microbes. High turnover rates of intermediate valence sulfur compounds and the intermittent availability of oxygen in these systems greatly impact the activity of sulfur‐oxidizing micro‐organisms in particular. In this study, the thiosulfate‐oxidizing hydrothermal vent bacteriumThiomicrospira thermophilastrain EPR85 was grown in continuous culture at a range of dissolved oxygen concentrations (0.04–1.9 mM) and high pressure (5–10 MPa) in medium buffered at pH 8. Thiosulfate oxidation under these conditions produced tetrathionate, sulfate, and elemental sulfur, in contrast to previous closed‐system experiments at ambient pressure during which thiosulfate was quantitatively oxidized to sulfate. The maximum observed specific growth rate at 5 MPa pressure under unlimited O2was 0.25 hr−1. This is comparable to theμmax(0.28 hr−1) observed at low pH (<6) at ambient pressure whenT. thermophilaproduces the same mix of sulfur species. The half‐saturation constant for O2() estimated from this study was 0.2 mM (at a cell density of 105cells/ml) and was robust at all pressures tested (0.4–10 MPa), consistent with piezotolerant behavior of this strain. The cell‐specificwas determined to be 1.5 pmol O2/cell. The concentrations of products formed were correlated with oxygen availability, with tetrathionate production in excess of sulfate production at all pressure conditions tested. This study provides evidence for transient sulfur storage during times when substrate concentration exceeds cell‐specificand subsequent consumption when oxygen dropped below that threshold. These results may be common among sulfur oxidizers in a variety of environments (e.g., deep marine sediments to photosynthetic microbial mats).

 
more » « less
PAR ID:
10460639
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Geobiology
Volume:
17
Issue:
5
ISSN:
1472-4677
Page Range / eLocation ID:
p. 564-576
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Summary

    Chemotrophic microorganisms gain energy for cellular functions by catalyzing oxidation–reduction (redox) reactions that are out of equilibrium. Calculations of the Gibbs energy (ΔGr) can identify whether a reaction is thermodynamically favourable and quantify the accompanying energy yield at the temperature, pressure and chemical composition in the system of interest. Based on carefully calculated values ofΔGr, we predict a novel microbial metabolism – sulfur comproportionation (3H2S ++ 2H+4S0+ 4H2O). We show that at elevated concentrations of sulfide and sulfate in acidic environments over a broad temperature range, this putative metabolism can be exergonic (ΔGr<0), yielding ~30–50 kJ mol−1. We suggest that this may be sufficient energy to support a chemolithotrophic metabolism currently missing from the literature. Other versions of this metabolism, comproportionation to thiosulfate (H2S ++ H2O) and to sulfite (H2S + 34+ 2H+), are only moderately exergonic or endergonic even at ideal geochemical conditions. Natural and impacted environments, including sulfidic karst systems, shallow‐sea hydrothermal vents, sites of acid mine drainage, and acid–sulfate crater lakes, may be ideal hunting grounds for finding microbial sulfur comproportionators.

     
    more » « less
  2. Abstract

    A graphGis said to be 2‐divisible if for all (nonempty) induced subgraphsHofG,can be partitioned into two setssuch thatand. (Heredenotes the clique number ofG, the number of vertices in a largest clique ofG). A graphGis said to be perfectly divisible if for all induced subgraphsHofG,can be partitioned into two setssuch thatis perfect and. We prove that if a graph is‐free, then it is 2‐divisible. We also prove that if a graph is bull‐free and either odd‐hole‐free orP5‐free, then it is perfectly divisible.

     
    more » « less
  3. Abstract

    Raman scattering is performed on Fe3GeTe2(FGT) at temperatures from 8 to 300 K and under pressures from the ambient pressure to 9.43 GPa. Temperature‐dependent and pressure‐dependent Raman spectra are reported. The results reveal respective anomalous softening and moderate stiffening of the two Raman active modes as a result of the increase of pressure. The anomalous softening suggests anharmonic phonon dynamics and strong spin–phonon coupling. Pressure‐dependent density functional theory and phonon calculations are conducted and used to study the magnetic properties of FGT and assign the observed Raman modes,and. The calculations proved the strong spin–phonon coupling for themode. In addition, a synergistic interplay of pressure‐induced reduction of spin exchange interactions and spin–orbit coupling effect accounts for the softening of themode as pressure increases.

     
    more » « less
  4. Abstract

    Serendipitous measurements of deep internal wave signatures are evident in oscillatory variations around the background descent rates reported by one model of Deep Argo float. For the 10,045 profiles analyzed here, the average root‐mean‐square of vertical velocity variances,, from 1,000 m to the seafloor, is 0.0045 m s−1, with a 5%–95% range of 0.0028–0.0067 m s−1. Dominant vertical wavelengths,λz, estimated from the integrals of lagged autocorrelation sequences have an average value of 757 m, with a 5%–95% range of 493–1,108 m. Bothandλzexhibit regional variations among and within some deep ocean basins, with generally largerand shorterλzin regions of rougher bathymetry or stronger deep currents. These correlations are both expected, since largerand shorterλzshould be found near internal wave generation regions.

     
    more » « less
  5. The genusOreochromisis among the most popular of the tilapiine cichlid tribe for aquaculture. However, their temperature and hypoxia tolerance, if tested at all, is usually tested at temperatures of 20–25°C, rather than at the considerably higher temperatures of 30–35°C typical of tropical aquaculture.

    We hypothesized that both larvae and adults of the heat and hypoxia‐adapted Tabasco‐line of the Nile tilapiaOreochromis niloticuswould be relatively hypoxia‐tolerant. Oxygen consumption rate (), Q10and aquatic surface respiration (ASR) was measured using closed respirometry at 2 (c. 0.2 g), 30 (c. 2–5 g), 105c. (10–15 g) and 240 (c. 250 g) days of development, at 25°C, 30°C and 35°C.at 30°C was inversely related to body mass:c. 90 μM O2g−1/h in larvae down toc. 1 μM O2g−1/h in young adults. Q10forwas typical for fish over the range 25–35°C of 1.5–2.0. ASR was exhibited by 50% of the fish at pO2of 15–50 mmHg in a temperature‐dependent fashion. However, the largest adults showed notable ASR only when pO2fell to below 10 mmHg. Remarkably, pcritforwas 12–17 mmHg at 25–30°C and still only 20–25 mmHg across development at 35°C. These values are among the lowest measured for teleost fishes. Noteworthy is that all fish maintain equilibrium, ventilated their gills and showed routine locomotor action for 10–20 min afterceased at near anoxia and when then returned to oxygenated waters, all fish survived, further indicating a remarkable hypoxic tolerance. Remarkably, data assembled forfrom >30 studies showed a > x2000 difference, which we attribute to calculation or conversion errors. Nonetheless, pcritwas very low for allOreochromissp. and lowest in the heat and hypoxia‐adapted Tabasco line.

     
    more » « less