title: Whole cell kinetics of ureolysis by Sporosarcina pasteurii.
abstract: OBJECTIVE
  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) NH4+ and (iv) pH (H(+) activity).
  
  
  RESULTS
  Batch ureolysis rate experiments were performed with suspended cells of S. pasteurii and one parameter was varied in each set of experiments. A Michaelis-Menten model for urea dependence was fitted to the rate data (R(2)  = 0·95) using a nonlinear mixed effects statistical model. The resulting half-saturation coefficient, Km , was 305 mmol l(-1) and maximum rate constant, Vmax , was 200 mmol l(-1)  h(-1) . However, a first-order model with k1  = 0·35 h(-1) fit the data better (R(2)  = 0·99) for urea concentrations up to 330 mmol l(-1) . Cell concentrations in the range tested (1 × 10(7) -2 × 10(8)  CFU ml(-1) ) were linearly correlated with ureolysis rate (cell dependent Vmax' = 6·4 × 10(-9)  mmol CFU(-1)  h(-1) ).
  
  
  CONCLUSIONS
  Neither pH (6-9) nor ammonium concentrations up to 0·19 mol l(-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.
  
  
  CONCLUSIONS
  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.
authors: Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA.|Department of Civil Engineering, Montana State University, Bozeman, MT, USA.
authors: E G
authors: EG
authors: Lauchnor
authors: Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA.|Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT, USA.
authors: D M
authors: DM
authors: Topp
authors: Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA.|Department of Mathematical Sciences, Montana State University, Bozeman, MT, USA.
authors: A E
authors: AE
authors: Parker
authors: Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA.|Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT, USA.
authors: R
authors: R
authors: Gerlach
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002119:Calcium Carbonate / Q000737:chemistry / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D058644:Sporosarcina / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D014508:Urea / Q000737:chemistry / Q000378:metabolism*; D014510:Urease / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D014508:Urea; D014510:Urease; D002119:Calcium Carbonate
keywords: Michaelis-Menten model; Sporosarcina pasteurii; ammonium inhibition; microbial kinetics; pH inhibition; ureolysis