Fig. 2

a The bacterial growth of S. pasteurii cultivated TSB with urea (red), and without urea at pH 7.4 (black), and without urea at pH 9.0 (blue) in 40 h were measured. With the removal of residue urea in the preculture medium, the bacterial growth of S. pasteurii is showed in green line. The intracellular urease activity b, ammonium concentration (c, red line) and pH of bacterial suspension (b, black line) of S. pasteurii cultivated with urea and without urea in 40 h were measured. The morphology of S. pasteurii cultivated with urea (+) and without urea (−) d was observed by SEM. The trend of zeta potential of S. pasteurii cultivated with urea was compared to that without urea e at different time points. All scale bars are 2 μm. The weight of precipitation produced by S. pasteurii cultivated with urea and without urea at 12 h or at OD₆₀₀ = 1 f were compared. NU meant that no extra urea was added during the process of mineralization