Isolation And Application Of Acinetobacter Calcoaceticus P13 In Mitigating Cropping Obstacle Of Cucumber

Continuous cropping obstacles is an agriculture problem that many countries needs to solve.Studies show,the accumulation of phenolic acids harm to crop development and it is one of the primary causes of continuous cropping obstacles in plants.Ferulic acid（FA）,p-hydroxy benzoic acid（PHBA）are the main phenolic acids material in the soil and toxic substances of many plants.In this study,we isolated a bacterium strain which can degrade FA and PHBA.Then we applied the inoculants which made using this bacterium strain to the soil containing FA and PHBA.We studied the mechanism of degradation of ferulic acid and P-hydroxybenzonic acid through the changes of cucumber development and rhizosphere soil enzyme activities after applying the inoculants to the soil.The main results are as follows.（1）We isolated a bacterium strain which high-effectively degrade the FA and PHBA.We identified the bacterium strains as a bacteria named Acinetobacter calcoaceticus P13 by using molecular biology techniques.We named P13 in this study.We tried to use this strain to alleviate the continuous cropping obstacles caused by FA and PHBA,which laid the foundation for developing the inoculants for degrading the FA and PHBA.（2）We confirmed the medium depending on the percentage of FA and PHBA in the seven years of continuous cropping cucumber soil.HPLC analyzed the products from the degradation reaction.The main metabolite were 4-Vinylguaiaco1,vanillic acid,vanilline and protocatechuic acid when the FA is degraded by P13.And when the PHBA is degraded by P13,the main metabolite was protocatechuic acid.Then,the best conditions were KH₂PO₄21.59g/L,pH 6.96,39.37?C.With this conditions,the degradation rate of FA and PHBA could reach by the 74.29%and 72.36%in the 2 hours respectively,and all completely degraded in the 3hours.In the process of degrading the FA and PHBA by Acinetobacter calcoaceticus P13.CAT,SOD,APX and other antioxidant enzymes in bacteria changed,which could lay the foundation for researching the degradation mechanism.（3）The inoculants made from P13 were applied to the soil with a certain proportion of exogenous FA,PHBA and then the physiological experiments were performed.This experiment divided basically same cucumber seedling into four treatment groups.they are Control,P13,PHBA+FA and PHBA+FA+P13.The results show that the contents of MDA,O₂.^-and H₂O₂ in cucumber leaves were higher after adding FA to the soil,while the activities of CAT,SOD,APX and other antioxidant enzymes were reduced.Thus,we concluded that adding inoculants can effectively alleviate the stress caused by FA and PHBA.（4）The activities of alkaline phosphatase,urease,sucrase and catalase in the soil of experimental group with Acinetobacter calcoaceticus P13 applied in simulated continuous cropping cucumber soil were improved and the metabolism of soil organic matter were enhanced.Besides,the removal efficiency of harmful substances were also increased,which could remove excess phenolic acids and improve soil microbial consortia structure.Thus,Acinetobacter calcoaceticus P13 could alleviate the stress induced by FA and PHBA,and promote the growth of cucumber.In a conclusion,we isolated a strains named Acinetobacter calcoaceticus P13 which has ability in degrading FA and PHBA.Adding the strains in soil could improve the physiological indicators of cucumber under the stress caused by FA and PHBA,and repaire the soil with continuous cropping obstacles,which lay the foundation for the development of mixed inoculants used for degrading the FA and PHBA.