Microbes Enhance The Phytoremediation For Heavy Metal Contaminated Soil

The human health and food safety is threatened with heavy metalcontaminated soil, which is attracting the international researchers’attention. It’s a potential method that microbes enhance thephytoremediation of heavy metals contaminated soil. But the microbes’quality directly affects the efficiency of phytoremediation. The researchof microbes’ effect in phytoremediation of heavy metal contaminated soilhas great significance for human survival.The contents of heavy metals in the soil at five sampling sectionsaround one of the smelters beside Xiangjiang River including Cd, Pb, Cr,Cu, Zn, Ni and Hg were detected. The results of the test were evaluatedwith Nemerow’s single and comprehensive factor pollution index andHakanson’s ecological risk index which were subsequently studied ontheir similarities and differences as well. The outcomes show that the soilis polluted heavily by Cd, slightly by Pb, and also polluted by Zn and Hg,but there is almost no pollution from Cu, Ni and Cr. The results from thespatial distribution of heavy metals show that the section A is heavilypolluted and has high ecological risk. Compared with other sections, thesection D, polluted slightly, is about4km from smelters and far awayfrom the living area. The pollution degree of section B, C and E isbetween the level of A and D. Due to the heaviest contaminated by heavymetals, the vertical distribution of heavy metals at section A is analyzedthoroughly. The findings show that heavy metals cause different degreesof contamination and ecological risk in soil layer. The upper soil layer(0-30cm) is polluted heavier than others, in which Cd content (7.52mg·kg-1) is12.1times of40-100cm soil layer’s. The pollution source isreveal by studying the spatial distribution of heavy metals in soil. Theheavy metal pollution is caused by the human industrial activities inrecent years. The heavy metals root in the deposition of smelter’s flue gasand the waste water irrigation, which enrich in the upper soil layer (0-30cm) and pollute the soil and crops. From all the above, we select sectionA for further research that microbes enhance the phytoremediation ofheavy metal contaminated soil.The metal-resistant strains which can normal grow in the concentration of4mmol L-1Cd,50mmol L-1Cu and50mmol L-1Cumedium were isolated from metal contaminated soil around the smelterbeside Xiangjiang River in China. Then sidorophores-producing bacteria(SPB) H1were screened out using the modified Chrome Azurol S(CAS)-agar plate from metal-resistant strains. Based on thecharacterizations of the Physiological and biochemical characteristics16SrDNA sequence analysis, strain H1was identified as Pseudomonas. TheH1strains named as Pseudomonas sp. H1, which have99%similarity toPseudomonas sp. RE*1-1-14(NC020209.1) in Genbank. The type ofsidorophore is identified by ultraviolet-visible spectra, which is similar to2,3-DHBA. However, compared with the chemical construction of2,3-DHBA, the sidorophore type has added amino-acid chains on it. Under274.0nm fluorescence excitation, the product of H1with strong emissionpeak in548nm. On the other hand, acids-producing funguses (APF) Su1and CMC enzymes-producing funguses Su2were screened out inmetal-resistant strains. Su2has strong capacity to produce acid. Itscapicity to produce citric acid increased by36.5%reaching to0.7389g L-1after its fermentation process was optimized. The influencingfactors of CMC enzyme activity of Su2were optimized, including thecarbon source, nitrogen source, carbon nitrogen ratio and initial pH inferment liquid. ITS homology analysis shows that Su1is similar withPenicillium aculeatum strain H23(gb|GU566285.1|) and the homology upto98%. We named it as Penicillium aculeatum Su1and Su2was namedas Aspergillus fumigatus Su2.At last, the capacity of above strains to mobilize heavy metals (Cu,Cd, Pb) in soil was detected. The Exchangeable/carbonate phases (E&C),Adsorption to Fe/Mn oxides (F&M), Organics and sulfides fractions(O&S), Residues (RES) and Water soluble states (WS) of Cu, Cd and Pbwere analyzed by the modified Community Bureau of Reference (BCR)sequential extraction procedure. The E&C concentrations account for70%of total Cd, about10%of total Cu and14%of total Pb.Pseudomonas sp. H1has the stronger ability to mobilize E&C heavymetals Cu and Cd, all E&C Cu and Cd can be dissolved in solution.Especially for Cd mobilizing ability, it can dissolve90%of total Cd in soil. But, it has weak capacity to mobilize Pb. The ability of Penicilliumaculeatum Su1to mobilize all the metals (Cu, Pb and Cd) is strong,especially Cd.In a conclusion, Pseudomonas sp. H1and Penicillium aculeatum Su1strains can produce siderophores or acids and have the excellentmetal-mobilizing capacity. It may solve the bottleneck problem of lowbioavailability of heavy metals and low biomass of hyperaccumulatorplants in phytoremediation of polluted soil. Aspergillus fumigatus Su2isexpected to be used in plant straw degradation for phytoremediation ofheavy metal polluted soil, which can recycle heavy metals in the plantbody easily.