Whole cell kinetics of ureolysis by Sporosarcina pasteurii
E. G. Lauchnor, D. M. Topp, A. E. Parker, R. Gerlach
Journal of Applied Microbiology
Aims Ureolysis drives microbially induced calcium carbonate precipitation (MICP). MICP models typically employ simplified urea hydrolysis kinetics that do not account for cell density, pH effect or product inhibition. Here, ureolysis rate studies with whole cells of Sporosarcina pasteurii aimed to determine the relationship between ureolysis rate and concentrations of (i) urea, (ii) cells, (iii) inline image and (iv) pH (H+ activity). Methods and Results Batch ureolysis rate experiments were performed with suspended cells of S. pasteurii and one parameter was varied in each set of experiments. A Michaelisâ€“Menten model for urea dependence was fitted to the rate data (R2 = 0Â·95) using a nonlinear mixed effects statistical model. The resulting half-saturation coefficient, Km, was 305 mmol lâˆ’1 and maximum rate constant, Vmax, was 200 mmol lâˆ’1 hâˆ’1. However, a first-order model with k1 = 0Â·35 hâˆ’1 fit the data better (R2 = 0Â·99) for urea concentrations up to 330 mmol lâˆ’1. Cell concentrations in the range tested (1 Ã— 107â€“2 Ã— 108 CFU mlâˆ’1) were linearly correlated with ureolysis rate (cell dependent inline image = 6Â·4 Ã— 10âˆ’9 mmol CFUâˆ’1 hâˆ’1). Conclusions Neither pH (6â€“9) nor ammonium concentrations up to 0Â·19 mol lâˆ’1 had significant effects on the ureolysis rate and are not necessary in kinetic modelling of ureolysis. Thus, we conclude that first-order kinetics with respect to urea and cell concentrations are likely sufficient to describe urea hydrolysis rates at most relevant concentrations. Significance and Impact of the Study These results can be used in simulations of ureolysis driven processes such as microbially induced mineral precipitation and they verify that under the stated conditions, a simplified first-order rate for ureolysis can be employed. The study shows that the kinetic models developed for enzyme kinetics of urease do not apply to whole cells of S. pasteurii.
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