Screening Highly Efficient Degradation Strains Of Allelochemicals And Ralstonia--solanacearum Biological Control

O-phthalic acid and its product phthalic acid ester(PAEs)have infiltrated into food,medicine,human body,food and medicine bottle packaging products,water body and terrestrial ecosystems,which have caused great harm to ecosystem and human health,and are regarded as universal pollutants in the world.The enrichment of o-phthalic acid and its derivatives in soil is an important substance that leads to continuous cropping obstacles and soil-borne diseases and insect pests of important cash crops such as tobacco,soybean,maize and,and has caused serious economic losses.Eliminating the harm of o-phthalic acid and its esters to the environment,human beings and crops is one of the hot spots in the field of environmental protection.Methods of eliminating o-phthalic acid and its esters mainly are physical,chemical and biological.Physical and chemical methods are not widely applied because of the risk of secondary pollution and the limited treatment of o-phthalic acid and its esters in industrial wastewater.However,biological methods,especially the use of microbes to degrade o-phthalic acid and its esters,have attracted much attention.In microorganisms,phthalic acid ester is first hydrolyzed to phthalate monoester,then hydrolyzed to o-phthalic acid,and finally degraded into organic acids to provide nutrition for microbes.Therefore,the main characteristics of the degradation of o-phthalic acid to phthalic acid ester by microorganism are high efficiency,low cost and environment-friendly.Screening or domesticating PAEs highly efficient degradation strains from the environment is the most simple and economical way.At present,the main highly efficient degradation bacteria are Arthrobacter sp,Pseudomonas sp.and so on.All of these mono bacteria have defects such as single substrate and incomplete degradation.Although the complex bacteria group overcomes the defect of substrate singleness,improves the degradation efficiency to a certain extent.However,most of the studies focus on the degradation of phthalic acid esters,regardless of single strain or complex bacteria group,and little attention was paid to the degradation of o-phthalic acid,which may be the cause of the highest content of o-phthalic acid in soil environment.In addition,most of the previous studies were limited to shaking flask fermentation in laboratory,and there were few reports on whether degradation bacteria could still play a role in soil environment.Moreover,microorganisms in soil environment are regarded as the largest biological diversity library in nature,containing more efficient o-phthalic acid and its esters degradation bacteria.Based on the above reasons,the microorganisms that can specifically degrade o-phthalic acid,p-hydroxybenzoic acid and p-hydroxybenzaldehyde were screened from sludge of sewage treatment plant and tobacco field of continuous cropping.The degradation ability of corresponding allelochemicals,the changes of tobacco seedling growth and antioxidant enzyme activities in tobacco leaves were tested in liquid medium and basin soil after the addition of allelochemicals.With And it had inhibition effect on Ralstonia solanacearum.The results are as follows:[1]The strains that could degrade o-phthalic acid,p-hydroxybenzoic acid and p-hydroxybenzaldehyde were screened and identified by physiological,biochemical and molecular biological identification,and named Enterobacter sp.N03,Stenotrophomonas sp.NO10 and Bacillus sp.N013 respectively.[2].Through the single factor experiment to get that the optimum pH for Enterobacter sp.N03 was 7 and the temperature was 30 ?,the initial concentration of o-phthalic acid was 500 mg/L;the optimum pH for Stenotrophomonas 5p.NO 10 was 6 and the temperature was 30 ? the initial concentration of p-hydroxybenzoic acid was 600 mg/L;the optimum pH for Bacillus sp.NO 13 was 8 and the temperature was 37 ?,the initial concentration of p-hydroxybenzaldehyde was 700 mg/L.[3]In the pot experiment,all the degradation bacteria of o-phthalic acid,p-hydroxybenzoic acid and p-hydroxybenzaldehyde could alleviate the inhibitory effect of the accumulation of o-phthalic acid,p-hydroxybenzoic acid and p-hydroxybenzaldehyde on tobacco.[4]The chemotactic effect experiments showed that o-phthalic acid and p-hydroxy benzaldehyde could attract the ralstonia solanacearum and made them gather in the accumulating place of o-phthalic acid and p-hydroxybenzaldehyde.[5]The results of pot experiment showed that the number and incidence of ralstonia solanacearum of tobacco increased in the soil accumulated with o-phthalic acid,p-hydroxybenzoic acid and p-hydroxybenzaldehyde,and the number and incidence of ralstonia solanacearum of tobacco decreased after adding corresponding degrading bacteria.[6]The results of pot experiment showed that adding allelochemicals caused the change of anti inverse enzyme activity in leaves,and the enzyme activity was restored after adding the corresponding degrading bacteria...