## 2 Materials and Methods
### Experimental Setup  
Experimental variants are summarized in Table 2. Experiment A (455 days) involved several variants of periodic bioaugmentation using a mixture of _Ochrobactrum_ sp. and _Bacillus_ sp. and biostimulation using BSM as a source of mineral nutrients. Significantly shorter experiment B (45 days) involved single initial bioaugmentation with _G. rubripertincta_ CWB2 and _R. erythropolis_ S43 and biostimulation with siderophore desferrioxamine B (DFOB).  
Contaminated soil (2 kg per pot for Experiment A and 0.5 kg per pot for Experiment B (less soil in experiment B was used because we did not have enough soil from the same sampling) was placed in a series of 2-L plastic pots. Four replicates were prepared for each variant. The soil was mixed manually each week in order to provide aeration. Experiments were carried out in an air-conditioned laboratory with constant temperature (25 \({}^{\circ}\)C \(\pm\) 1.0 \({}^{\circ}\)C).  
\begin{table}
\begin{tabular}{c c} \hline \hline  & **Set-Up, Maintenance** \\ \hline Experiment A & 2.0 kg soil, periodic addition of \(\dots\) \\ \hline AC (control) & Distilled water only \\ AA (bioaugmentation) & _Bacillus_ sp. + _Ochrobactrum_ sp. suspended in water \\ AS (biostimulation) & Mineral nutrients BSM \\ AD (combination) & _Bacillus_ sp. + _Ochrobactrum_ sp. suspended in mineral nutrients medium (BSM) \\ \hline Experiment B & 0.5 kg soil, initial addition of \(\dots\) \\ \hline BC (control) & water (60 mL) \\ BD (DFOB) & 2 mM Desferrioxamine (60 mL) \\ BG1 (Fe\({}^{2*}\)) & _G. rubripertincta_ CWB2 + 60 mL Fe\({}^{2*}\)-containing BSM \\ BG2 (no Fe) & _G. rubripertincta_ CWB2 + 60 mL Fe-free BSM \\ BG3 (Fe\({}^{3*}\)) & _G. rubripertincta_ CWB2 + 60 mL Fe-free BSM + FeCl\({}_{3}\) (5 g\(\cdot\)kg\({}^{-1}\) soil) \\ BR1 (Fe\({}^{2*}\)) & _R. erythropolis_ S43 + 60 mL Fe\({}^{2*}\)-containing BSM \\ BR2 (no Fe\({}^{2+}\)) & _R. erythropolis_ S43 + 60 mL Fe-free BSM \\ BR3 (Fe\({}^{3*}\)) & _R. erythropolis_ S43 + 60 mL Fe-free BSM + FeCl\({}_{3}\) (5 g\(\cdot\)kg\({}^{-1}\) soil) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Description of experimental variants.  
Soil humidity of experiment A was maintained at 10-15% (m/m) through a weekly addition of either distilled water, mineral nutrients solution (i.e., BSM), suspension of microorganisms or their combinations. Details are summarized in Table 2. Concentrated suspension was prepared from the culture, which was perpetually grown in fermenter as described in Section 2.2. An aliquot of 300 mL was withdrawn from a fermenter (average OD\({}_{600}\) 0.60 \(\pm\) 0.17), centrifuged at 4000 rpm for 10 min and split into equal parts. This inoculum was then resuspended in 37.5 mL of sterile BSM or sterile water (see Table 2 for details), inoculated into the soil and the soil was mixed. For non-inoculated variants AC and AS the same volume (37.5 mL) of sterile distilled water or sterile BSM was used respectively (Table 2).  
Experiment B was set-up in the beginning only. _G. rubripertincta_ CWB2 was grown to OD\({}_{600}\) = 0.23, _R. erythropolis_ S43 to OD\({}_{600}\) = 0.14, the suspensions from all Erlenmeyer flasks (6 \(\times\) 60 mL) were put together, separated into three centrifugation tubes, centrifuged (4000 rpm, 10 min), resuspended in appropriate media (Table 2) and inoculated. The humidity was maintained at 10-15% (m/m) by weekly addition of distilled water.