Screening Of Biosurfactant-producing Bacterial Strains And Their Effects On The Uptake Of Lead And Cadmium In Soils By Plants

Phytoremediation is a relatively safe, economic and easily operated and promisingtechnology to remove heavy metals from soil. Low biomass of plants and low availabilityof heavy metals in soil limit the efficiency of phytoremediation. The effectivephytoremediation includes suitable plants choice and available heavy metal increase insoils. However, phytoremediators, the plants used for remediation, generally grow slowly,having small biomass and difficulty to absorb and enrich fixed HMs in soils. And severalstudies have showed that chelating agents such as ethylene diamine triacetic acid (EDTA)and citric acid can be used to increase metal mobility in soil, thereby enhancingphytoextraction. But EDTA is expensive and could cause heavy metal pollution inunderground water. Bacteria were thought to play import roles in promotion of plantgrowth and heavy metal uptake in heavy metal-polluted soils, Therefore, it is veryimportant to search for a microbe-strengthened phytoremediation approach to enhancephytoremediation economically.Biosurfactant-producing strains T4, J3, J119, R, Q1, U and C1 were screened out from61 soil samples. Strain J119 was primarily identified as Erwinia sp., T4 and J3 wereidentified as Pseudomonas. And the biosurfactant produced by Strain J119 was primarilyidentified lipopeptide, the biosurfactants produced by T4 and J3 were glycolipid. Theresults of the influence of the temperature, pH, osmolality, heavy metals and antibiotics onthe growth of the strains showed that strains T4, J3 and J119 could grow at temperature4℃to 37℃and pH 4.0 to 9.0. The optimum growth temperature and pH for J119 were28℃and 5.5, and for T4 and J3 were 37℃and 7.2. Strain T4, J3 and J119 grew well in themedium containing 5% NaCl. Strain J119 could resist Pb, Cd and various antibiotics.The soil experiment indicate that 7 biosurfactant-producing strains all can activateprecipitate Pb and Cd in soil, and the concentrations of exchangeable Pb and Cd in soiladding fermentation were higher than control. The effect of Strain J119 fermentation was best, in the soil (PbCO₃ 200,400,800mg kg^-1), the concentrations of exchangeable Pbwere increased by14.6%, 59.1%å’Œ39.6%; in the soil(CdCO₃50, 100, 150mg kg^-1), theconcentrations of exchangeable Cd were increased by 70.3%, 65.7%å’Œ7.5%.Theexperiment that the different day fermentation of strain J119 and 3 suffactants activateprecipitate PbCO₃ and CdCO₃ and fixed Pb and Cd in soil show for 1-5d fermentation ofstrain J119 the activation efficiency were increased day by day, and no significantdifference of the activation efficiency for 4-8d fermentation of strain J119 were existed.The effect of 5d fermentation on activate Pb was better than the synthetic surfactant ofCTAB, SDS, Tween-80,but The effect on activate Cd was approximate to 5d fermentationand the synthetic suffactant of CTAB,SDS,Tween-80.In flask-shaking tests, PbCO₃,CdCO₃ and Pb(NO₃)₂, CdSO4 were respectively added into the liquid fermentation mediumfor investigating the effect of biosurfactant-producing strain J119 and 3 synthetic surfactanton activation of hardly-soluble Pb and Cd in solutions. The results showed that strain couldobviously increase the concentration of lead and cadmium ions in solutions. In mediuminoculated the test strains, the concentrations of Pb²⁺ and Cd²⁺ were increased by158.49%and 98.41%, and Significant difference of the concentrations of Pb²⁺ and Cd²⁺between the treatment of inoculation and the synthetic surfactants of CTAB,SDS,Tween-80 were existed, in the medium (Pb 200,400,800mg kg^-1), the concentrations ofPb²⁺ were increased by151.8%, 149.6% and 125.4%; in the medium(Cd 50,100,150mgkg^-1), the concentrations of Cd²⁺were increased by 260.0%,269.9% and 365.5%.The 6 plants Brassica campestris, Zea mays, Pennisetum alopecuroides, Sorghumsudanense, Lycopersicon esculentum and Solanum melongena were chose for pot test,Matched relationship between strain J119 and the 6 plants was investigated, the resultsshow that at inoculation treatments polluted single Pb the dry weight of Brassicacampestris, Zea mays, Sorghum sudanense, Lycopersicon esculentum and Solanummelongena were increased by 5.8%,11.4%,28.8%,23.3% and 7.8%, the concentration ofPb in shootof Brassica campestris and roots of Brassica campestris, Pennisetumalopecuroides and Sorghum sudanense were increased by 31.0%,35.0%,28.0% and 19.0%respectively, compared to the control.; at inoculation treatments polluted single Cd the dryweight of Brassica campestris, Zea mays, Lycopersicon esculentum and Solanumraelongena were increased by 24.8%,25.0%,22.3% and 14.0%, the concentration of Cdin shoots of Brassica campestris, Zea mays, Sorghum sudanense, Lycopersicon esculentum and Solanum melongena and their roots were increased by 43.0%,34.0%,7.0%,32.0%,110.0% and 740.0%,23.0%,6.0%,20.0%,8% respectively, compared to the control., andthe accumulation coefficient of the shoots of the Brassica campestris, Lycopersiconesculentum and Solanum melongena were 2.87,1.81,2.02. In solution experiments therelative conductivity in roots of Lycopersicon esculentum, Brassica campestris and Indiamustard increased markedly due to the addition of the fermentation and the supernatant ofstrain J119 and the synthetic surfactants of CTAB,SDS,Tween-80, but no liner relationshipbetween the relative conductivity and the concentration of Pb and Cd are existed, the typeof surfactant maybe play a key role, the effects of nonionic surfactant Tween-80 and thefermentation and the supernatant of strain J119 on promoting Lycopersicon esculentum,Brassica campestris and India mustard absorbing Pb and Cd were better than SDS andCTAB.