| Phytoremediation is an emerging as a cost-effective and environment-friendlytechnology for remediation of heavymetal-contaminated soils. However, phytoremediators,the plants used for remediation, often have a slow growthrate and produce limited amountsof biomass. Using chemicals to enhance phytoremediation is comparatively available butusually expensive and unfriendly to environment. Therefore, it is very important to searchfor a microbe-strengthened phytoremediation approach to enhance plant remediationeconomically.Bacterial strain G10, G16 and B5 were isolated from root of plants. They were capableof promoting rape and wheat growth either in the presence or absence of Pb2+ or Cd2+. Thethree strains were primarily identified as Pseudomonas sp.(G10), Brevibacterium sp.(G16) andAzotomonas sp.(B5), respectively, based on their morphological and physio-biochemicalcharacteristics.All the strains produced indole acetic acid (IAA), isopentenyl adenosine (iPA) orsiderophores, and they contained the enzyme 1-aminocyclopropane-1-carboxylate (ACC)deaminase, which hydrolyses ACC (the immediate precursor of plant hormone ethylene) toNH3 and a-ketobutyrate. Besides, strain G10 exhibited the capability of solubilizinginorganic phosphate and antagonism against Sclerotinia sclerotiorum or Rhizoctoniacerealis. Strain G16 and B5 were able to fix nitrogen. The results of the influence of thetemperature, pH, osmolality, heavy metals and antibiotics on the growth of the strainsshowed that strains G10, B5 grew well at temperature 7℃to 37℃and pH 5.0 to 10.0.The optimum growth conditions were: temperature 28℃, pH 7-9. All strains could growwell in the medium containing 5% NaCl. Strain G10 could grow in the medium added Pb2+(200mg·L-1), Cd2+ (20mg·L-1), Zn2+ (100 mg·L-1), Km (20 mg·L-1), Amp (100 mg·L-1),Str (20 mg·L-1), Spe (20 mg·L-1) and G16 could grow in the medium added Pb2+ (200mg·L-1), Cd2+ (20 mg·L-1), Cu2+ (50 mg·L-1), Ni2+(20 mg·L-1), Zn2+ (100 mg·L-1), Km (20mg·L-1), Amp (100 mg·L-1), Spe (20 mg·L-1). Strain B5 showed tolerance to Pb2+ (200 mg·L-1), Cd2+ (20 mg·L-1), Cu2+ (50 mg·L-1), Zn2+ (100 mg·L-1), Km (20 mg·L-1), Amp(100 mg·L-1), Str (20 mg·L-1), Tc (20 mg·L-1) and Spe (20 mg·L-1). Experiments onactivation of PbCO3 and CdCO3 showed that the contents of available Pb in solutionsinoculated with strains were 131-328μg·L-1more than that of controls while the pH valueswere decreased to 7.32 (G10), 7.28 (G16) and 7.69 (B5) from 8.65; the contents ofavailable Cd in solutions inoculated with strains were 69.95-359.65 mg·L-1 more than thatof controls while the pH values were decreased to 4.68 (G10), 5.55 (G16) and 5.39 (B5)from 7.20. Furthermore, the strains were able to produce suffactant.The three strains labeled by rifampicin were used to inoculate seeds of rape, which weresowed in Pb and Cd-supplemented soils. After 30 days, strain G10 and G16 were isolatedsuccessfully from roots of rape, and the three strains have colonized well aroundrhizosphere. The pot experiments clearly demonstrated the beneficial effects of strains onthe plant growth. Plant dry weights were significantly affected (P＜0.05) by strains, andincreased by 6.4-77.7% (shoot) and 2.9-149.1% (root). Bacterial inoculations produced upto 3.0-81.4% (shoot) and 5.6-43.7% (root) increase in the efficiency of lead phytoextractionby rape. Cd concentrations within plant tissues were increased by 3.0-24.8% (shoot) and11.2-77.7% (root) afte rinoculated with strains, too. The strains stimulated rape biomassproduction and, hence, its phytoextraction. The contents of available Pb, Cd anddissolubility sugar in the soils inoculated with strains were increased, while the pH valuesof rhizosphere soil were decreased compared with the uninoculation control. Therefore, thethree strains had efficacy in rape rhizosphere and could strengthen phytoremediation inmoderate HM contaminated soils.
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