Screening Of Cadmium-tolerant Plant Growth Promoting Rhizobacteria And Optimization Of Spore Production Condition

The results of the 2014 national soil pollution survey showed that the cadmium pollution was the highest level in soil heavy metal pollution.Soil cadmium pollution has become one of the major environmental problems in China.Compared with traditional phytoremediation,plant-microbial combined remediation can enhance the enrichment of plants.And the key to achieve the progress of combined bioremediation technology is to obtain highly effective microorganisms that interact with hyperaccumulator.Bacillus is an important component of plant rhizosphere-promoting bacteria.It is highly resistant to stress,environmentally friendly,and widely used in fields,which is an ideal joint repair material.This study is to screen cadmium tolerant plant growth promoting rhizobacteria for the growth and cadmium accumulation of Solanum nigrum L.,directionally screen the cadmium-resistant bacillus by heat-treated,investigate the interaction between the strain and the Solanum nigrum L.by hydroponic experiment to determine the optimal combination of plant-microbe,and optimize the sporulation condition of PGPR.This study can provide material support for microbial-phytoremediation of cadmium polluton in farmland,and provide theoretical basis for the preparation of agricultural microbial agents.The main research results of this subject are as follows:1.Isolation of cadmium-tolerant PGPR from Solanum nigrum L.rhizosphere soil and directional screening of Bacillus by heat treatment.9cadmium-tolerant PGPR were isolated from Solanum nigrum L.rhizosphere soil,in which.5 strains are Bacillus spp..They are Lysinibacillus boronitolerans WT4,Lysinibacillus sp.NT1,Bacillus badius QT3,Bacillus megaterium NCT-2 and Bacillus subtilis WT5.2.The effects of strains on plant growth and cadmium enrichment ability were studied by hydroponic experiment under 4 mg/kg cadmium stress.As the result,NT1 strain can promote the growth of plant.Compared with CK-Cd,the plant height increased by 31.33%,the dry matter of aboveground increased by 62.65%and the dry matter of underground increased by 28.10%.It can enhance the cadmium accumulation of plant,cadmium accumulation increased by 28.52%and54.61%in aboveground and underground parts spectively,compared with CK-Cd.It can reduce the content of MDA,reduce the damage caused by cadmium stress,increase the content of total chlorophyll and enhance photosynthesis.3.The biological characteristics of NT1 strain were studied.The gram staining is positive.It has elliptic or oval spores,located in the center or extreme of the bacteria,which is not swell.The colony is yellowish,opaque,smooth and smooth.It has motility,and the cells were rod-shape,with a width of 0.7-1.2?m and a length of 2-4?m.The optimum pH is 7,the optimum temperature is 37?,and the logarithmic phase of growth is4-16 h.4.The optimum formulation of NT1 sporulation fermentation medium was determined by central composite design as follows:bran10.90 g/L,peanut cake powder 18.17 g/L,KH₂PO₄ 0.53 g/L,MgSO₄ 0.59g/L,MnSO₄ 0.07 g/L,CaCO₃ 0.12 g/L.The maximum value of sporulation number is 1.5×10¹00 CFU/mL.