2.3. Measurement of urease activity and calcite production
Experimental conditions were the same as for the bacterial mixtures
growth described above. To establish the bacterial mixtures,
first, a bacterial culture was added to the experimental flasks and
incubated at 30 ◦C for 24 h with continuous agitation at 200 rpm.
Urease activity was determined using the phenol-hypochlorite
assay (Natarajan, 1995). The bacterial suspension (250 L) was
added to 250 L of 0.1 M sodium phosphate buffer containing
500 L of 3 M urea solution. The mixture was incubated at
37 ◦C with regular time intervals. Subsequently, 2 mL of phenol
nitroprusside solution were added to an alkaline hypochlorite solution
and, then, incubated at 50 ◦C for 40 min. After incubation,
absorbance was measured at 626 nm with ammonium chloride
(0–10 M) as a standard. One unit of urease activity was defined
as the amount of enzyme that catalyzed the hydrolysis of 1 M
urea per min.
To produce calcite,the isolates were cultured inYAbrothfor 24 h
and subcultured onto BPU broth (3 g/L beef extract, 5 g/L peptone,
and 20 g/Lurea at pH 7) at 30 ◦Cfor 72 h withcontinuous agitationat
200 rpm. The bacterial suspension (500 L) was added to 500 L of
350 m