The main objective of this research was to investigate the effects of chromium upon microbial community structure over time. The experiments were conducted on a previously uncontaminated soil amended with various levels of hexavalent Cr. Only 2-3% of the Cr was bioavailable 10 days after addition of the metal. Even though Cr bioavailability decreased rapidly, the bacterial community richness, as measured using denaturing gradient gel electrophoresis (DGGE), was reduced for both the 200 and 1000 mg kg-1 Cr treatments. One year after contamination, bacterial community richness had not returned to pre-disturbance levels. However, the fungal community had increased richness for the Cr-contaminated soils that was maintained for the duration of experiment. Changes in bacterial community richness were significantly related to both the total amount of Cr added and Cr bioavailability. From this research, there appears to be an antagonistic relationship between the fungal and bacterial communities stressed by Cr, which is significantly related to the total metal in the system. Due to technical problems with the amplification of DNA isolated from these chromium containing soils, I hypothesized that Cr was extracted along with the DNA isolated directly from soil. Using size exclusion chromatography with inductively coupled plasma mass spectrometry (SEC-ICP-MS), I determined the DNA extracts contained Cr. However, Cr was not free in solution indicating that inhibition of PCR was related to the environmental DNA samples containing low levels of Cr (0.5-0.7 ng g-1). To further understand the impact of Cr bound to DNA, DNA from an eight member model bacterial community was extracted in the presence of varying concentrations of Cr and community structure was measured using DGGE. The DGGE profiles of the DNA extracted in the presence of Cr had decreases in the number of bands corresponding to the model community, as well as decreases in the intensity of individual bands, as Cr concentrations increased. These results indicate that PCR-based molecular analyses of metal containing DNA may indicate altered community profiles that do not reflect actual changes in the community.
|School:||University of Cincinnati|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/10(E), Dissertation Abstracts International|
|Keywords:||Bacterial community, Dgge, Fungal community, Sec-icp-ms|
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