Study On The Ability Of Cadmium-tolerant Enterobacter To Dissolve Cadmium And Promote Growth

With the abundance of agricultural chemicals and the development of industrialization,cadmium pollution in agricultural soil has become a serious environmental problem.Engineering measures in the field of physical chemistry have obvious and stable effects in controlling heavy metal pollution in soil,but they are only suitable for small areas of heavily polluted soil due to their high cost,large investment and easy to cause problems such as weak soil fertility.Phytoremediation has attracted extensive attention because of its low cost,benefits to improve soil ecological environment,and can reduce secondary pollution.However,due to its long plant growth cycle,small biomass and many growth constraints,phytoremediation cannot achieve the ideal remediation effect.It is a research direction to effectively enhance phytoremediation to promote plant growth through mechanisms such as growth promotion and biocontrol of rhizosphere microorganisms,and at the same time metabolize and produce acid to promote dissolution of heavy metals and improve bioavailability of heavy metals so as to promote absorption of heavy metals by enriched plants.Therefore,on the basis of five strains of Enterobacter bacteria which have strong cadmium tolerance,this paper further studied the cadmium solubility of five strains of bacteria.And took three vegetables: rape,sweet bamboo mustard and Indian mustard as test objects,through germination rate test and pot culture experiment under different media and cadmium stress environment,then screened the strains which have obvious growth promoting effect under heavy metal stress.Expected to obtain the strains which can be actually applied to soil remediation and provide practical basis for the development of bacterial fertilizer for plant-microorganism remediation.According to 16 s r DNA squencing,the five strains 12,13,14,19,25 identified were most similar to Enterobacter bacteria.The 5 strains have strong cadmium dissolving ability,and the cadmium dissolving rate reaches 54% ? 68% after culturing in a medium supplemented with cadmium carbonate.The cadmium dissolution rates of b12,b13,b14,b19 and b25 after rifampicin induced resistance of the strain are between 45% and 80%,and there is no obvious difference between the cadmium dissolution rates of the corresponding strain before induction,and the strain has stable cadmium dissolution performance.Five strains have different promotion effects on the germination rate of rape,sweet bamboo mustard and Indian mustard.Among them,strain 12,13 and 19 have significant promotion effects on the germination rate of rape,strain 13,14,19 and 25 have significant promotion effects on the germination rate of sweet bamboo mustard,and five strains have no significant promotion effect on the germination rate of Indian mustard.Under the condition of potted plant without adding cadmium and perlite,strain 12,strain 13 and strain 14 significantly increased the fresh weight of Indian mustard,increasing the yield by 17.40%,20.74% and 16.04% respectively,while the biomass of rape and sweet bamboo mustard was not significantly promoted by five strains of bacterium.Under the condition of perlite potted plant containing 100 mg/L cadmium,strain 14 showed a growth promoting trend on fresh weight of rape,increasing yield by 15.92%,and five strains had no obvious effect on sweet bamboo mustard and Indian mustard.Under the condition of adding cadmium to soil pot culture,strain 14 has significant growth promoting effect on Indian mustard,with the highest yield,fresh weight increased by 3.58 times compared with the control.strain 14 and 19 have an increasing trend on fresh weight of rape,increasing yield by 25.6% and 12.28% respectively.In potted plants with different cadmium concentrations(0.3,20 and 100 mg/kg),the fresh weight of Indian mustard treated with no cadmium and the dry weight of Indian mustard treated with 100 mg/kg were significantly higher than the corresponding non-inoculation treatment.In the compound strain construction test,there was no significant difference in the cadmium dissolution rate between the inoculated three fungi and the control of the sterilization medium,and there was no significant difference in the cadmium dissolution ability between the inoculated b14 and strain b14 mixed with the fungus.In low phosphorus sucrose medium,there was no significant difference in cadmium dissolution rate between inoculated three kinds of strains and sterilized medium control.The cadmium dissolution rate of strain b14 was significantly higher than that of strain b14 alone after being compounded with Bacillus megaterium and Bacillus licheniformis respectively.There is no antagonistic reaction between strain b14 and decomposed bacteria,and a composite microbial agent can be constructed.The results of simulated composting test with compound microbial inoculum containing b14 showed that the cadmium dissolving efficiency of the compost product inoculated in the early stage was the highest,reaching 24.6%.In addition,b14 was cultured in different media containing cadmium.It was found that Lysogeny broth and low phosphorus media had different effects on the acid-producing and cadmium-dissolving ability of the strain.Among the components of Lysogeny broth,peptone and Yeast extract had obvious inhibitory effects on acid-producing of the bacterial liquid.