Article Figures & Data
Figures
- FIG. 1.
Sample raw data collected during the continuous-feeding experiments for paired bioreactors inoculated with cells or abiotic oxides. Data are from the run started on 9 May 2001. (A) Dissolved oxygen concentrations. (B) Rate of continuous Fe(II) addition. When Fe(II) pulses were added by syringe, the continuous-feed Fe(II) pumps were turned off. (C) Dissolved Fe(II) concentrations. Note that higher rates of Fe(II) addition to the live-cell bioreactor did not typically result in higher Fe(II) concentrations.
- FIG. 2.
Sample growth curves for BrT. The dates are the inoculation dates for the bioreactor runs. (A) Typical growth curves from several bioreactor runs. (B) Effect of Fe(II) supply on cell growth. Cell density did not increase in the absence of an Fe(II) supply.
- FIG. 3.
Sample plots of [Fe(II)] versus time during pulse-feeding experiments. Oxidation rates were calculated by determining the slope of [Fe(II)] versus time when the Fe(II) concentrations were >100 μM.
- FIG. 4.
Variations in modeled Fe(II) oxidation rates with changes in [O2], [Fe]total, and the Fe(II) addition rate. For clarity, standard deviations are shown only for the model output obtained at 0.5% O2 and 1 mM [Fe]total and at 3.0% O2 and 10 mM [Fe]total. (A) Biotic oxidation rates. (B) Secondary effects on abiotic oxidation rates. Negative values imply that the dead cells or cellular by-products inhibited chemical oxidation rates. (C) Net effect of cells on total Fe(II) oxidation rates, expressed as the percentage of change compared with the value for the no-cell treatment. Positive values indicate that the cells increased the total oxidation rate.
Tables
- TABLE 1.
Cell growth data for BrT
Inoculation date Feeding mode Doubling time (h) Maximum cell density (cells ml−1) 13 December 2000 Pulse 33.3 ± 3.8 2.1 × 106a 16 January 2001 Pulse 22.9 ± 5.8 1.3 × 107 20 February 2001 Pulse 23.6 ± 7.9 9.8 × 106 28 March 2001 Continuous 30.5 ± 2.4b 1.8 × 107 9 May 2001 Continuous 16.7 ± 3.0 1.4 × 107 - TABLE 2.
Microbial contribution to total Fe(II) oxidation—direct measurementa
Date Fe(II) oxidation rate (μM h−1) % Biotic Before azide addition After azide addition 20 February 2001 63 43 32 13 March 2001b 81 59 27 28 March 2001 314 256 18 9 May 2001 885 414 53 ↵ a Unless otherwise indicated, all data are for strain BrT. Biotic Fe(II) oxidation was measured directly by determining the difference between successive oxidation rate measurements in the same bioreactor. The first run contained live cells (before azide addition; biotic plus abiotic oxidation) and was followed by a run with killed cells (after azide addition; abiotic oxidation only).
↵ b Data for the marine Fe(II) oxidizer JV-1.
- TABLE 3.
Multiple linear regression model parametersa
Treatment m1 m2 m3 b r2 Live cells 10.47 (4.67)A 0.0020 (0.0007)B 0.843 (0.020)B −20.46 (12.53)D 0.989 Killed cells 15.56 (4.95)A 0.0110 (0.0032)A 0.577 (0.097)A −49.15 (14.47)A 0.919 No cells 15.30 (6.82)B 0.0026 (0.0013)C 0.700 (0.047)A −11.91 (11.22)D 0.916 ↵ a The Fe(II) oxidation rate (r) [micromolar Fe(II) oxidized per hour] is calculated as follows: r = m1 × [O2] + m2 × [Fe]total + m3 × [Fe(II) addition rate] + b, where the units for [O2] are the percentage of air saturation, the units for [Fe]total are micromolar, and the units for Fe(II) addition rate are micromolar per hour. The values in parentheses are standard deviations. Also shown is the regression coefficient for each model (r2). The letters after the values indicate the significance of each term to the regression model, as follows: A, P < 0.001; B, P < 0.01; C, P < 0.05; D, not significant.
- TABLE 4.
Microbial contribution to total Fe(II) oxidation—statistical modelinga
[O2] (% of air saturation) [Fe]total (mM) Fe(II) addition rate (μM h−1) Fe(II) oxidation rate (μM h−1) % Biotic Total Biotic 0.5 1 100 71 44 62 600 493 177 36 0.5 10 300b 257 16 6 600 511 96 19 3.0 1 100 97 31 32 600 519 165 32 3.0 10 300b 284 3 1 600 537 83 16 ↵ a Total and biotic Fe(II) oxidation rates were calculated as described in the text.
↵ b At Fe(II) addition rates of <300 μM h−1, the modeled biotic oxidation rates with an [Fe]total of 10 mM were negative; under these conditions, the biotic contribution to total Fe(II) oxidation could not be calculated.
