## 3 Methods
### Micro-Tests after the Addition of B. pasteurii to CG and FA  
To discover the effect of CG and FA environments on the mineralizing capacity of _B. pasteurii_ at the micro-level, they were added separately to the basic culture medium in two different tubes, also containing urea. The tubes, named FA group_1 and CG group_2, respectively, were placed in a shaker at a constant temperature of 30 \({}^{\circ}\)C. In this shaker, a third tube, considered as reference group_0, was also present. It contained the same basic culture medium of _B. pasteurii_ and the same amount of urea, but without the presence of CG and FA. The compositions of the three groups used for micro-tests are shown in Table 2. From each tube, a 0.3 mL sample was extracted seven times (after 0 h, 6 h, 12 h, 24 h, 36 h, 48 h and 60 h) to be immediately subjected to a bacterial concentration test and a urea hydrolysis test. This procedure was repeated three times. The optical density (OD) test, based on the turbidity of the culture, was used to measure the _B. pasteurii_ biomass concentration. Monitoring bacterial growth dynamics is routinely performed in a wide range of areas, and due to its relative ease of implementation, the OD measurement is widely adopted for this purpose. By utilizing the OD method, bacterial concentrations are approximated indirectly through changes in light scattering within the sample [37]. This approach provides real-time data on bacterial density, enhancing the utility of _B. pasteurii_ across various industrial contexts. The maximum absorption peak (at \(\lambda\) = 645 nm) was obtained by full wavelength scanning [38] of _B. pasteurii_ in a basic culture medium using a spectrophotometer (Puxi, China). A blank (uninoculated culture \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Components** & **Reference\_0** & **FA Group\_1** & **CG Group\_2** \\ \hline CG (g) & 0 & 0 & 1 \\ FA (g) & 0 & 1 & 0 \\ Culture medium (mL) & 5 & 5 & 5 \\ _B. pasteurii_ (mL) & 0.1 & 0.1 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Compositions of the three groups for micro-tests. medium) was used to calibrate the spectrophotometer prior to measuring the OD of the three groups. Subsequently, 0.3 mL was taken from the bacterial culture and transferred into a 10 mm cuvette to undergo a tenfold dilution. Finally, the density was measured with the above-mentioned spectrophotometer. After adding urea to each group, conductivity tests, performed by means of a conductivity meter (Thermo Scientific Orion 410C-06A, Thermo Scientific, Waltham, MA, USA), detected when the _B. pasteurii_ was producing urease (i.e., hydrolyzing urea and providing CO\({}_{3}\)\({}^{2-}\)) to be used in the subsequent mineralization reactions. Inside the tubes, a precipitation generation experiment was carried out to exclude conductivity increases due to other factors or experimental errors, as well as to provide a multifaceted view of the mineralization phenomenon. A pre-test was first conducted to check whether a visible precipitation occurs immediately after the addition of CaCl\({}_{2}\) at a later stage of incubation (at least after 36 h). Accordingly, to clearly and visually observe the onset of mineralization of _B. pasteurii_ in the CG and FA groups, respectively, CaCl\({}_{2}\) was added at different times (chosen according to the results of the urea hydrolysis test). The precipitation samples were observed at various magnification levels using scanning electron microscopy (SEM; Sigma series; Zeiss, Jena, Germany). A thin layer of gold was sprayed on the samples to increase the electrical conductivity. In addition to SEM, energy-dispersive X-ray spectroscopy (EDS; X-Max 20; Oxford Instruments, Oxfordshire, UK) was used to identify the chemical elements of the samples. To determine the presence of biominerals in the precipitation samples, a Bruker Vertex 80 V spectrophotometer was used to record the FTIR spectra (with the wavenumber ranging from 4000 to 400 cm\({}^{-1}\)).