NOCARDIA SP. STRAIN SJJ-8-7 ISOLATED FROM A KARST CAVE IN SOUTHWESTERN CHINA PRECIPITATES CALCIUM CARBONATE.

Bacterial calcium carbonate precipitation in caves is a general phenomenon. To better understand the specific process of bacterial calcium carbonate precipitation, we inoculated Nocardia sp. strain SJJ-8-7 and strain SJJ-8-7 mixed with unidentified strain SJJ-2-3(the mixed strain) to experimental system of simulation drip water. Strain SJJ-8-7 and strain SJJ-2-3 were isolated from Shijiangjun cave, a karst cave in Guizhou Province of southwestern China. Strain SJJ-8-7 and the mixed strain were cultured in B-4C medium (improved from B-4 medium with 1:2 Mg/Ca mass ratio) and D-4 medium (similar B-4C medium without yeast extract). Experiments of simulation drip water were monitoring with a duration of 34 days. The temporal variations both of the Ca or Mg concentration of the mediums and the pH values of the mediums were measured by inductively coupled plasma optical emission spectrometry (ICPOES) and a pH meter, respectively. The composition of mineral elements, crystal characteristics and carbon isotope information of bacterial calcium carbonate precipitation were detected. The results demonstrated that strain SJJ-8-7 and the mixed strain would have greatly promoted the pH value of the liquid medium along with the growth and reproduction of the bacteria till 8th day. Then tends to a stable value. The Ca concentration of the solution gradually decreased down to minimum until the 15th day. Thus, Ca will be a large number of removal with the pH value of a substantial increase, thereby promoting the occurrence of deposition. Mg did not change with the regularity. This suggested that it is a physiological adaptation of bacteria removal toxic Ca by mineralization, but it is an inevitable choice in Carich oligotrophic karst caves. The crystals of the bacterial sediments are calcite in the experiments system of simulation drip water. The precipitates of a variety of morphological features including spherical and rhombic, rod, ellipsoid and irregular forms were greatly observed in the microbial systems by scanning electronic microscopy but not in the chemical system. There were some bacterial-like escape pores in the crystal of microbial precipitation. Furthermore, the microbial sediments have more negative carbon isotope information than the cave secondary deposits, while the microbial sediments under the dynamic simulation system have more negative carbon isotope information than understanding culture. We suggested that bacterial induceed carbonate precipitation which may provide a new way to explain the abnormal distribution of carbon isotopes. [ABSTRACT FROM AUTHOR]