cultures were then aerobically incubated at 25 ºC for
30 d. The evolution of pH and calcium concentration
were monitored throughout the experiment after 0, 4,
7, 21 and 30 d. pH was measured with a pHmeter Basic
20 /Crison) and calcium concentration was measured
with a Perkin-Elmer 5100ZL atomic absorption
spectrophotometer with flame photometry, graphite
camera and automatic analyzer equipment. Precipitates
were removed by centrifugation of the media and the
sediments were re-suspended and washed in distilled
water to free of impurities. The washed carbonate
crystals were finally air-dried at 37 ºC. A control
consisting of uninoculated culture media and media
inoculated with autoclaved cells (dead cells) were
included in all experiments.