Using PCR-DGGE and Soil Respiration to Characterize Bacterial Changes in Heavy Metal Contaminated Soils

Soil contamination to heavy metals such as lead and zinc in and around mines causes a change in structure, complexity, diversity and activity of soil microbial communities like bacteria. In the present research, PCR-DGGE approach was used to investigate the effects of Pb and Zn-contamination in Bama mine near Isfahan city on bacterial diversity, structure and complexity. Basal Respiration (BR) and Substrate Induced Respiration (SIR) was also used to assess microbial activities. Nine samples from three locations (3 for each) with different levels of heavy metal contamination were taken (from low to high), then their DNA were directly extracted. Also a 468 base pair of their 16S rRNA genes were amplified using specific primers, and their fingerprints were obtained by denaturing gradient gel electrophoresis (DGGE). BR and SIR were measured, and metabolic quotient was calculated. Finally, soil microbial activity in polluted conditions was achieved. Our findings illustrate that heavy metal contamination has negative effects on bacterial diversity. By increasing the bioavailability of Pb and Zn, the complexity and diversity of bacterial communities decreased and the frequency of resistant bacteria increased. By increasing Pb and Cd contamination, SIR reduced and this shows the reduction in microbial biomass. In these conditions, SIR and metabolic quotient was more sensitive than BR, so they are better ecological indicators in polluted soils.
Discussion and Although bacterial diversity showed reduction in polluted soils, diversity is still relatively high. Bacterial ability to adapt in heavy metal contamination, bacterial resistance and their important functional roles in such conditions are valuable in soil ecosystem suggesting further researches on them.