Fig 1.
Conceptual flow of the microbial biomining process.
Bacterial treatment (1) makes the material more magnetic by reducing iron. A magnet is applied to extract the magnetic material (2), and those particles are 3D printed and sintered (3). The material is then ready for construction, maintenance, and repair applications (4).
Table 1.
Overview of the regolith simulants used and experiments performed in this paper.
Table 2.
Average major metal oxide composition (wt%) at different Mars locations [29–31] and the composition of three different regolith simulant types obtained via X-ray fluorescence (XRF) as well as reported by the suppliers (JSC-Mars1 [32], JSC-2 [23], EAC-1 [23]).
Table 3.
X-ray diffraction analysis of the Mars Rocknest soil [21] and the three different regolith simulants.
Fig 2.
Evaluation of the toxicity of different Lunar and Martian regolith simulants to S. oneidensis under aerobic and anaerobic conditions.
Colony forming units (CFU/μL) are depicted on the left axis and the O.D.600 measurements on the right axis. The yellow, blue, red, green, and grey bars represent regolith concentrations of 0, 0.1, 1, 10, and 100 g/L respectively. Optical density at 600 nm of control samples without S. oneidensis were subtracted from the O.D.600 measurements. The error bars represent the standard error of the mean. Aerobic growth behavior of Shewanella oneidensis was measured in the presence of JSC-Mars1 (A), EAC-1 (C) and JSC-2A (E), and anaerobic growth of Shewanella oneidensis was measured in the presence of JSC-Mars1 (B), EAC-1 (D) and JSC-2A (F).
Fig 3.
Aerobic extraction of magnetic material and determination of aqueous ferrous iron concentration from EAC-1 (blue), JSC-2A (grey), and JSC-Mars1 (orange) regolith simulants.
The darker color in each plot represents the bacterial sample, the lighter one the non-bacterial control. (A) The set-up for small-scale magnetic extraction. In short, 1 mL sample (1) was pipetted into a cuvette, then the magnetic fraction was extracted via a magnet, washed in a MilliQ water (2), and finally dried in a previously weighed cuvette (3). The weight difference of the cuvette before and after this treatment represents the extracted magnetic material. (B) Absorbance of Fe(II) iron standards bound to 1,10-Phenanthroline in the absence and presence of Fe(III). O.D.510 was measured for a range of 0–200 ppm Fe(II)(aq) with or without a constant concentration of 100 ppm Fe(III)(aq). (C, E, G) The weight of magnetically extracted material from samples containing 10g/L EAC-1 (C), JSC-2A (E), or JSC-Mars1 (G) solution with and without S. oneidensis after 0h and 168h. An increase of the magnetically extractable material was measured for all of the bacterially treated samples (n = 6). (D, F, H) Absorbance of the colorimetric iron determination of 10 g/L EAC-1 (D), JSC-2A (F), and JSC-Mars1 (H) treated with aerobic S. oneidensis over 168 hours. A consistent increase of the Fe(II)(aq) concentration was measured for all of the bacterially treated samples (n = 9). Mean plus standard deviation is shown for the bar plots (One-way ANOVA with Tukey PostHoc test: N.s. > 0.05; * ≤ 0.05; ** ≤ 0.01; *** ≤ 0.001).
Fig 4.
Anaerobic extraction of magnetic material from bacterially treated JSC-Mars1 regolith simulant.
The amount of magnetically extracted material from a 10g/L JSC-Mars1 regolith simulant anaerobically incubated with (red) or without (orange) Shewanella bacteria in TSB medium (A) or defined minimal medium (MM) (C) after 0h, 72h, and 168h. The O.D.510 values of the colorimetric assay to determine the Fe(II)(aq) concentration of 10 g/L JSC-Mars1 regolith anaerobically incubated with (red) or without (orange) Shewanella bacteria in TSB medium (B) and defined minimal medium (D). The standard deviation is given for all bar plots (One-way ANOVA with Tukey PostHoc test: N.s. > 0.05; * ≤ 0.05; ** ≤ 0.01; *** ≤ 0.001). (E) X-ray photoelectron spectroscopy of iron in JSC-Mars1 regolith samples. A change is visible in the Fe(II) and Fe(III) satellite peaks between the 0h (black line) and the 168h (red line) timepoints of incubation with S. oneidensis.
Fig 5.
X-ray fluorescence spectroscopy analyzing the (A) iron concentration (wt%) and (B) silicon concentration (wt%) of the three different regolith simulants as given by the supplier (“supplier”, shown in bright colors); measured without treatment (untreated, in intermediate colors); or bacterially treated and magnetically extracted (treated, in dark colors). The different regolith types are indicated in blue for EAC-1, grey for JSC-2A, and red for JSC-Mars1. Error bars display the standard deviation.
Fig 6.
Lithography-based ceramic manufacturing (LCM) prints of JSC-2A regolith-based materials.
(A) Lithography-based ceramic manufacturing of the regolith simulant JSC-2A (B) The ultimate compressive strength (UCS) of untreated (n = 9) and the bacterially treated and magnetically extracted material (n = 5). Error bars are displayed as standard deviation (Student’s t-test: N.s. > 0.05; * ≤ 0.05; ** ≤ 0.01; *** ≤ 0.001).