Reduced Heavy Metals Accumulation Of Crops In The Presence Of Heavy Metal Resistant And Plant Growth-Promoting Bacteria And Their Preservation Technology

With the rapid development of industry,the extensive use of chemical pesticides and fertilizers,heavy metal contamination in farmland in China has become increasingly serious.Through a variety of mechanisms,a large number of heavy metal contaminants got into the farm ecosystem,which not only affect the productivity and quality of crops,but also endanger the animal and human health through the food chain.Microbe assisted phytoremediation is a green,environmentally friendly,easy to operate and cost-effective technology to remediate heavy metal-contaminated soil.Plant growth promoting bacteria(PGPB)can promote plant growth and improve plant tolerance to heavy metals.In addition,they can affect metal bioavailability by complexation,adsorption,and then reducing plant uptake and transport of heavy metals.The functional strains that promoted the growth of plants and blocked the absorption of heavy metals were screened,which provided the experimental basis for the remediation of heavy metal-contaminaed farmland and the safe production of agricultural products.The fermentation and preservation technology of bacterial agents were studied for the functional strains in order to obtain the optimal growth conditions and fermentation medium of optimal composition and fermentation conditions for the functional strains.Heavy metal resistant and growth-promoting Rhizobium sp.T1-17,Bacillus megaterium H3,Exiguobacterium mexicanum S2-4,Myroides xuamwuensis TH-19 QX33 were screened.According to the short-term pot experiment,strain H3 was selected as the tested strain to study the effects on the vegetable growth and heavy metal uptake.Strains H3 and T1-17 could promote plant growth and reduce heavy metals uptake in the plants.The fermentation and preservation of microbial agents were studied with strains H3 and T1-17.The individual components of the basal fermentation medium were obtained by single factor test;the response surface methodology design was used for optimizing the content of each component,optimal culture conditions were obtained by optimization of fermentation conditions.Under the condition of different adsorption rates,optimum adsorption rate was selected by measuring the viable count of the strains.The results showed that strain H3 could significantly promote the growth of wheats,increase the biomass of above ground tissues(11.2-42.4%)and roots(11.6-48.1%),and reduce the Cd content in the edible tissues by 30.0-33.4%and 23.9-55.1%,respectively.Inoculation with the tested bacteria significantly increased the biomass of above-ground biomass by 36.3-59.4%and 24.1-30.7%,respectively,under Cd and Pb contamination condition.Strains H3 significantly reduced Cd content of the edible tissues of the two greens by 9.4-10.1%and 10.7-11.9%,respectively.Meanwhile,vitamin C content of the greens increased in the presence of strain H3.Strain H3 decreased DTPA-extractable Cd and Pb contents and increased organic matter content in the rhizosphere soils of the two greens compared to the controls.By single factor experiment,the carbon source of the fermentation medium was molasses,nitrogen source was ammonium sulfate,inorganic salts were magnesium sulfate and potassium hydrogen phosphate;the contents of the components of the fermentation medium were molasses 11.97 g L-1,ammonium sulfate 0.87 g L-1,magnesium sulfate 0.41 g L-1,sodium chloride 0.12 g L-1,dipotassium hydrogen phosphate 1.76 g L-1,Yeast extract 0.60 g L-1 by the response surface methodology design.Compared with the 50%adsorption rate and 100%adsorption rate,80%adsorption rate obtained the maximum number of viable bacterial counts after 90 days.