IAA-secreting Bacteria, Flu-degrading Bacteria Enhanced The Remediation Of Flu In Soils By Plant

Polycyclic aromatic hydrocarbons (PAHs), a class of POPs, were widely distributed in the environment. Most of PAHs were toxic, mutagenic and carcinogenic. Plant-microorganism combined remediation of PAHs was green and cheap, and had long been recognized as an effective method for removal of PAHs from soil. We studied the remediation effects and mechanisms of the fluoranthene contaminated soil with ryegrass combined with the IAA-secreting bacteria and/or fluoranthene-degrading bacteria, which had been ioslated from the soil.In this study, three species of IAA-secreting bacteria were isolated from the experimental soil, named as ZZ13, ZZ18 and ZZ21, respectively. After 24h’shaking (30℃, 180rpm), these strains could produce 46.67mg/L,53.47 mg/L and 59.81mg/L IAA. Besides, these strains also have the capability of saline-alkaline tolerance and phosphate-dissolving. Based on the 16S rRNA sequencing along with morphological features and physiological traits, ZZ13, ZZ18 and ZZ21 were identified as Bacillus cereuss Bacillus subtilis and Arthrobacter pascens, respectively.In order to promote these three strains’growth and improve the IAA production, a fermentative optimization experiment with single factor test was designed, based on incubation time, initial pH, ventilatory capacity, temperature and different carbon source as well as nitrogen source. Results showed that the best culture condition for both strains growth and IAA production are not the same. Overall, the optimal conditions of ZZ13 were initial pH of 6, liquid volume of 15 mL/150 mL, temperature of 28℃, and shaking time of 20h, besides, the best carbon and nitrogen sources were mannitol and yeast, respectively. And the IAA production of ZZ13 could reach a highest level of 95.28mg/L. The optimal conditions of ZZ18 were initial pH of 10, liquid volume of 45 mL/150 mL, temperature of 28 ℃, and shaking time of 15h, besides, the best carbon and nitrogen sources were mannitol and yeast, respectively. And the IAA production of ZZ18 could reach a highest level of 80.15mg/L. The optimal conditions of ZZ21 were initial pH of 6, liquid volume of 45 mL/150 mL, temperature of 28 ℃, and shaking time of 15h, besides, the best carbon and nitrogen sources were mannitol and yeast, respectively. And the IAA production of ZZ21 could reach a highest level of 92.31 mg/L,In this paper, one fluoranthene-degrading bacteria was isolated from petroleum contaminated soil, named Z21. The degradation rate of 50mg/L fluoranthene,50mg/L anthracene, 100mg/L phenanthrene and 25mg/L benzoapyrene were 57.63%,31.43%, 22.27% and 24.92% after 7days. Based on the 16S rRNA sequencing along with morphological features and physiological traits, Z21 were identified as Bacillus cereus.The optimum condition for fluoranthene degragation by strain Z21 in liquid culture was:the initial pH of the culture was 8, the incubation temperature was 35℃, fluoranthene concentrations was 25 mg/L,60mL liquid culture in 150mL flask. Addition of glucose could promote fluoranthene degragation of Z21. And the degradation rate of fluoranthene could reach the highest level of 74.79%.A pot experiment was conducted to investigate the effect of the IAA-produce strain and Flu-degrading strain on the fluoranthene removal from the contaminated soil. Eight different treatments were set, and they were (1) soil contaminated with Flu (CK); (2)soil contaminated with Flu and planted ryegrass (P); (3)soil contaminated with Flu and treated with the IAA-produce strain(I); (4) soil contaminated with Flu and treated with Flu-degrade strain (F); (5) soil contaminated with Flu and treated with the two strains (FI); (6)soil contaminated with Flu and treated with the ryegrass and the IAA-produce strain (IP); (7)soil contaminated with Flu and treated with the ryegrass and the Flu-degrade strain(FP); (8)soil contaminated with Flu and treated with the ryegrass and the two strains (FIP).Compared to the CK treatment, Flu concentrations in the other treatments were much lower. What’s more, the Flu concentrations in the soils after 60 days were lower than them in the soils after 30-day culture. Both of the strains could enhance the remediation effects individually, and the most removal rate was appeared when the two strains applied simultaneously, which was 75.98% after 60-day culture. The potential mechanisms were that the IAA-produce strain could enhance the Flu removal by stimulating the plant biomass and the tolerance, and then the plant could have a better absorption of Flu. However, the PAH-degrade strain could directly utilize the Flu as a carbon resource and reduce the Flu concentration in the soil.The two strains could enhance the ryegrass biomass. The Flu contents in roots in all the treatments were higher than them in the shoots, the Flu concentrations in ryegrass roots and shoots were both decreased after 60 days than them after 30-day culture. What’s more it could be known that the counts of soil bacteria, fungi and actinomyces were all higher than those in the CK treatment. However, the counts of soil fungi and actinomyces in the treatments applied with strain only were lower than the treatments treated with ryegrass and strain, but the counts of bacteria had the opposite result. With the culture time increase, the microbial activities in all the treatments were stimulated and the microbial activities in the treatments with strain only were higher than them in the treatments applied with the strain and ryegrass.