| Heavy metal pollution is a common problem faced by all countries in the world.In the remediation of heavy metal contaminated soil,biological remediation is a kind of economic remediation technology without secondary pollution,which has broad application prospects.Some resistant microorganisms in soil have great help to plant growth and bioenrichment of heavy metals.Through the study of the combined remediation of heavy metal contaminated soil by resistant microorganisms and plants,it is beneficial to provide a new effective way for the remediation of heavy metal contaminated soil.In this study,thallium-resistant microorganisms were screened from thallium-contaminated soil,and their species were identified by physicochemical properties and 16S r DNA molecular identification.Their ability of IAA producing,siderophore producing,ACC deaminase producing,biofilm producing and starch hydrolysis and tolerance to heavy metals and acidity were analyzed.Thallium uptake test,organic acid secretion test and infrared spectrum analysis were used to explore the effects of different factors on thallium uptake and resistance mechanism of bacteria,and to analyze the growth promoting effect of strains on rice and cabbage and their effects on thallium stress alleviating ability of cabbage.The results are as follows:(1)8 thallium-resistant strains were screened,among which strains 1-2-1 and 7-2-11 had the highest tolerance,they can tolerate 500 mg·L-1thallium stress in solid medium.The two strains of bacteria were taken as research objects,and the morphological,physiological and biochemical properties and 16S r DNA sequence analysis showed that the two strains were bacillus cereus and bacillus megaterium respectively,both of which were gram-positive bacteria.(2)Biological characteristics experiments showed that both strains had IAA production and ACC deaminase production capacity.The strain 1-2-1 also had siderophores production,film production and starch hydrolysis capacity.The acid resistance of the two strains were similar,,and they grew normally at p H?5.0.The growth curves of the two strains showed that strain 1-2-1 had low sensitivity to Tl and could quickly adapt to the environment in which Tl+was present.Both strains had high resistance to Tl(?)and Cd(?),and the strain 1-2-1 also showed high tolerance to Cu(?)and Zn(?)stress.(3)When Tl+concentration was low,the amount of Tl absorption by bacteria is increased with the increase of Tl+concentration.The optimum absorption conditions for strain1-2-1 were 3%inoculation amount and 1-1.5 h absorption time.The optimum absorption conditions for strain 7-2-11 were 2%inoculation amount and 1.5-2 h absorption time.There was little change in the spectra of the two strains before and after Tl+adsorption,and no new characteristic absorption peaks appeared.The absorption peaks representing amine,hydroxyl,amide and carboxyl groups shifted to some extent,indicating that amine,hydroxyl,amide and carboxyl groups all played an important role in the adsorption process.The secretion of four organic acids was detected during the 48h metabolism of two strains of bacteria.Tartaric acid was the most,followed by acetic acid and oxalic acid,and malonic acid was the least secreted.(4)Plant experiments showed that two strains can promote the growth of rice and cabbage in thallium containing environment,and play an important role in alleviating thallium stress.And the application of two strains of bacteria significantly increased the relative elongation of rice roots.At 5 mg·L-1Tl+stress,the fresh weight of above-ground and root and root length of cabbage increased with the inoculation of bacteria,and application of both strains of bacteria significantly increased thallium content of cabbage above-ground and roots. |
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