2.1. Cultivation method

S. pasteurii (ATTC 11859) was used as ureolytic microorganism as this strain has a very high specific ureolytic activity, its urease synthesis is not repressed by ammonium, has no known pathogenicity [²⁶] and is therefore the most common used strain for MICP. The strain was cultured in NH4‐YE medium as recommended by ATTC. The medium contained 15.75 g Tris buffer (Carl Roth GmbH), 10 g ammonium sulfate (Sigma Aldrich) and 20 g yeast extract (Carl Roth GmbH) per liter. For preparation of the medium, Tris buffer was adjusted to pH 9.2 and divided into two equal parts. Yeast extract and ammonium sulfate were dissolved separately each in one part. The solutions were autoclaved at 121°C for 20 min. After cooling, the solutions were combined under sterile conditions to obtain the final medium. For cultivation, 200 ml of NH4‐YE medium was placed in 500 ml Erlenmeyer flasks and inoculated with 1 v/v % of a pre‐culture that was grown overnight. Cultivation was performed at 120 rpm at 30°C. During the cultivation samples were taken under sterile conditions and the optical density (OD₆₀₀) was measured at a wavelength of 600 nm (Cary 60 UV‐Vis, Agilent Technologies, USA).