| A soil perfusion system was used to determine Zn immobilization by soil microorganisms in Rubicon sand (pH 5.9). A 17 mgkg('-1) (.26 mM) Zn solution (320 mL) was perfused through 12.5 g of gamma-irradiated (sterilized) or biologically active soil. Approximately 75% of the perfusate Zn was inactivated by chemical and physical mechanisms. The introduction of biologically active soil microorganisms and sterile nutrient broth into a sterile soil perfusion system resulted in an additional significant reduction in Zn concentration of the soil perfusate. The level of Zn in the perfusate of the sterile perfusion system remained constant (3.9 mgL('-1) of Zn) during the same 72 hour perfusion period where the Zn level in the perfusate of the biologically active (inoculated) system decreased to 0.7 mgL('-1) of Zn. The enhanced immobilization represented over 90% of the Zn from the perfusion solution indicating that microorganisms immobilized a fraction of Zn (15%) in addition to the activated by chemical and physical mechanisms.; A soil sample was obtained from the soil perfusion column after maximum fixation had been attained. This soil sample was diluted in sterile water and surface plated on soil extract agar containing ('65)Zn. After colonies of microorganisms developed, the agar plate was placed on Kodak film X-OMAR-AR or NO-SCREEN (NS-2T) for autoradiography. The colonies that accumulated sufficient levels of radioactive ('65)Zn to expose the X-ray film were identified by comparison with the developed film. The colonies were isolated, grown in pure culture, and reconfirmed as "zinc accumulators" by the autoradiographic plating technique on ('65)Zn enriched agar.; Most of the isolated Zn immobilizing organisms were fungi, identified as predominantly Penicillium species. Other Zn-immobilizing fungi were Fusarium, Paecilomyces, Cladosporium, Cephalosporium, Mucor, and Aspergillus spp. The most abundant Zn-immobilizing bacteria were spore-forming Bacillus spp., and another unidentified gram-positive rod. |
