Heavy Metal Content and Microbial Composition of the Rhizosphere of Eleusine Indica Within an Auto-Mechanic Workshop in Benin City, Nigeria

Abstract

Plant-assisted bioremediation holds promise for in-situ treatment of polluted soil. However, en-hancement of this process for successful phytoremediation processes requires a sound understand-ing of the complex interactions of the rhizosphere. The present study thus investigated the chemi-cal and microbial composition of rhizosphere of Eleusine indica in an auto-mechanic workshop in Benin City. A plot of 30 m x 30 m was randomly located on the workshop and ten subdivided into 9 sub-plots of 10m x 10m, each designated as Subplots A – I, respectively. Plants were counted in each of the sub-plots and density was recorded as number of plants per 100 m2. Soil samples were obtained from within the plant’s rhizosphere and at a distance of 2 m away from plant presence. Results showed that there was an average of 34 plant stands/100 m2. Heavy metals assayed showed mean compositions of 1720.7 mg/kg of Fe, 80.3 mg/kg of Zn, 0.36 mg/kg of Cr, 3.92 mg/kg of Ni, and a total hydrocarbon content of 1856.2 mg/kg. Heavy metal presence within the rhizosphere was higher compared to those of soil samples collected 2 m away from the rhizosphere. The bacte-ria isolates generally obtained in the mechanic workshop were Bacillus subtilis, Microccoccus lu-teus, Microccoccus varians, Pseudomonas putida, Achromobacter sp, Bacillus pumilis, Clostrid-ium sp. and Serratia marascens. The following fungal isolates were identified: Aspergillus flavus, Aspergillus niger, Fusarium solani, Penicillium sp., Geotrichum sp., Rhizopus sp. and Tricho-derma sp. Diversity and dominance indices calculated indicated a species richness of 0.332 for bacterial presence in the rhizosphere, and a dominance index of 0.489. For fungal species in the rhizosphere, species richness was 0.289 whereas dominance index was 0.528. The findings thus indicated that successful plant-assisted bioremediation involves interactions of the rhizosphere.