Bioremediation of heavy metal polluted soil using plant growth promoting bacteria: an assessment of response

Soil samples were collected from research farm of Ebonyi State University and mining site in Izzi Local Government Area (L.G.A) of Ebonyi State. Rhizobacteria from rhizosphere of maize were identified using molecular methods. Tolerance of the isolates to heavy metals was assessed using standard laboratory techniques. The heavy metal profile of the soil was determined using atomic absorption spectrophotometer (AAS). Ability of the PGPB to remediate heavy metal polluted soil was assessed with hot plate aqua-regiae digestion method. The isolates were identified as: Pseudomonas fluorescens strain 5113, Alcaligenes faecalis strain P156, Pseudomonas syringae HS191, Bacillus subtilis strain NBSL51 and Bacillus cereus strain 20 UPMNR. P. fluorescens exhibited maximum tolerance at different concentrations of metals while A. faecalis had minimum tolerance. The heavy metal profile of the soil was determined and expressed in ppm as lead (25.0), copper (2.4), chromium (1.2) and zinc (16.0). The Isolates remediated the heavy metals. P. fluorescens + B. cereus maximally degraded the metals with values of (Pb = 87.2%, Zn = 69.25%, Cr =67.5%) while B. cereus alone degraded 70.0% Cu. P. fluorescens + B. cereus is recommended for soil that is contaminated with chromium, lead and zinc while B. cereus is recommended for copper contaminated soils.