Screening Of Cadmium Resistant And ACC Deaminase-producing Bacteria And Their Potential In Reducing The Uptake Of Cadmium In Maize

The heavy metal cadmium pollution in the farmland soil has become more and more serious.Maize is one of the most important food crops in China,cadmium accumulates in the roots,stems and leaves of corn,not only harms the yield and quality of corn,but also affects the human health through the food chain.Plant in situ immobilization technique technology is currently the better choice for the treatment of mild pollution in soil and the restoration of heavy metals in agricultural soils.Plant growth-promoting rhizobacteria can not only promote the growth of plants through various ways,improve the tolerance of plants to heavy metal environments,but also reduce the uptakeand transport of heavy metal in plants by changing the forms of heavy metals in soil.The main objectives of the present study were: 1)to screen and characterize heavy metal resistant and plant growth-promoting rhizobacteria with ACC deaminase,2)to analyze the effect of strains on the reduce of Cd uptake and accumulation in plant.The desired results will be usful for accelerating the in situ remediation of heavy metal contaminated soil by plant growth-promoting rhizobacteria-plant combined remediation,and also provide theoretical basis and technical approach for production of safe agricultural products with high efficiency in metal contaminated soil.In this experiment,12 strains with ACC deaminase activity were obtained by enrichment culture and dilution plating method.Most of the strains also had the abilities to dissolve phosphorus,produce IAA,producesiderophore,and tolerate various heavy metals.12 strains possessing ACC deaminase were identified as Burkholderia spp.and Achromobacter spp.Fivestrains(Burkholderia territorii a3,Burkholderia Arboris c1,Burkholderia territorii h2,Achromobacter xylosoxidans A1 and Achromobacter xylosoxidans J1)were further studied through various growth-promoting characteristics,heavy metal tolerance and identification results.Among the 5 strains,A1 and J1 did not produce IAA,and the amounts of IAA produced by strains a3 and c1 were up to 43.9 and 53.4 mg? L-1.5 strains had the ability to produce siderophore in different levels,and phosphate-solubilizing ability is 2.75-173.91 mg.L-1,in which strain c1 has the strongest ability to release phosphorus.The ACC activities of strains a3,c1,h2,A1 and J1 were 1.500,0.234,2.022,0.552 and 3.804 ?mol ?-butyric acid· mg-1 protein·h-1 respectively.Strains Burkholderia territorii a3 and Burkholderia territorii h2 could grow on agar plates containing higher concentrations of copper,cadmium,lead and zinc.Five testedstrains had strong adsorption capacity for soluble Cd with an adsorption rate of 30.31%-88.62%.The growth and cadmium uptake of maize seedlings with the inoculation of strains a3,c1,h2,A1 and J1 with ACC deaminase activity were evaluated by hydroponic experiments.The results showed that for culture of 15 days,inoculation with strains h2 and A1 could significantly increase the biomass of root,stem and leaf of maize seedlings,and significantly reduce the root cadmium content of maize seedlings by 60.7% and 37.2%,compared with non-inoculated control,at 4mg?L-1 Cd treatment;,Inoculation with strains h2,A1 and J1 could significantly increase root,stem and leaf biomass of maize seedlings,and significantly reduce Cd content in roots and stems of maize seedlings in range of 40.6%-42.8%,24.9%-27.3% and 39.0%-70.8% at 8 mg?L-1 Cd treatmen;At 4 mg?L-1 Cd treatment for 25 days,the inoculation with strain a3 and h2 could increase the dry weight of root,stem and leaf of maize seedlings.The application of strain a3 significantly reduce the Cd concentration of roots,stems and leaves of maize by 26.5%,23.6% and 36.1%,respectively;The application of strain h2 significantly reduce the Cd concentration of roots and stems of maize by 63.6% and 29.6%;At 8mg?L-1 Cd treatment for 25 days,strain A1 could significantly increase the biomass of roots,stems and leaves of maize seedlings,and could reduce the Cd concentration in roots,stems and leaves of maize seedlings by 27.6%,34.4% and 68.9%,respectively.The effects of the tested strains on the biomass and cadmium uptake were evaluated in pot culture experiment.The test results showed that in the soil added 0.4 mg.kg-1 Cd,inoculation with the five tested strains was found to increase the root,stem and leaf biomass of maize and reduce the Cd concentration of root,stem and leaf in corn in rang of 5.9%-28.0%,11.2%-15.3%,7.0%-37.9%,10.9%-44.9% and 17.4%-44.9%;in the soil added,0.8 mg.kg-1 Cd,inoculation with strain h2 could significantly increase the biomass of maize roots,stems and leaves,and could significantly reduce the Cd concentration of maize roots,stems and leaves by 41.8%,43.1% and 40.9%,respectively.In addition,inoculation with strains a3,A1 and J1 significantly increased soil catalase activity of rhizosphere soil in rang of by 26.4%-71.6%,20.9%-27.8%,and 18.2%-52.0%,respectively;inoculation with strains a3,c1,h2,and A1 significantly increased sucrose activity by 13.1%-25.7%,29.1%-34.1%,14.4%-25.3%,and 6.9%-45.3%,respectively;strains a3 and c1 significantly increased protease activity by 21.3%-186.1% and 46.3%-137.3%,respectively.The application of five tested strains increased urease activity by 62.5%-212.5%(0.4 mg.kg-1 Cd)and 23.1%-200%(0.8 mg.kg-1 Cd).Compared with the uninoculated control,strains h2,A1,and J1 significantly decreased the exchangeable,organic matter bound Cd content.