Rhizosphere microbial diversity in PAH’s contaminated and uncontaminated soil

Abstract

The intrusive and expensive nature of soil cleanup technologies like excavation and incineration created a need to search for alternative remediation technologies. Rhizoremediation and its associated microorganisms has the potential to cleanup contaminated soil in a ‘non invasive’ and cost-effective manner. The literature cites many benefits of the technology if implemented correctly. However, there is still a lack of knowledge concerning the interaction of the plants and microorganisms that are responsible for degrading the organic pollutants. In this study, the potential for degrading Poly aromatic hydrocarbons (PAH’S) by rhizosphere bacteria was investigated. In addition, the hydrocarbon removal efficiencies of different plant rhizospheres were investigated. The metabolic and genetic profiles of soil bacteria in vegetated and non- vegetated soils were determined. The results of the removal efficiencies of different plant rhizospheres showed that the removal of hydrocarbons was more effective in soil vegetated by different plant species. By using co-occurring (different) plant species, hydrocarbons were removed faster than when monoplanted were used. The number of hydrocarbon degrading bacteria in the rhizosphere increased during rhizoremediation of PAH’s contaminated soil. Analysis of the functional and genetic diversity in PAH’s contaminated and non-contaminated rhizosphere and non-rhizosphere soil, using Biolog (physiological community level) and genetic diversity (polymerase chain reaction- denaturant gradient gel electrophoresis) was determined. The biolog did not revealed clear difference on substrate utilization profiles of the microbial communities in the rhizosphere and bulk soil. However, unlike the Biolog DGGE revealed slightly differences in both the metabolic and genetic profiles of the different soil samples. The study on the feasibility of seeding bacteria capable of colonizing and surviving on the rhizosphere showed that Pseudomonas putida successfully colonized the rhizosphere of Eleusine corocana. The number of P putida increased during rhizoremediation of PAH’s. These results suggest that bacteria with the ability to adhere and survive in the root zone can be engineered and seeded for rhizoremediation purposes. However, other factors such as the influence of soil type and organic matter content must be investigated to improve rhizoremediation technology.