Isolation, Identification And Characterization Of P-hydroxybenzoic Acid-degrading Bacterium From Cucumber Rhizosphere

Cucumber is one of main cultivated vegetables in our country, the continuous cropping pattern of greenhouse cultivation likely to lead to continuous cropping obstacle. P-hydroxybenzoic acid(PHBA) is one of the main autotoxin lead to continuous cropping obstacles. In this experiment, PHBA degraded bacterium were screened from the rhizospheric soil of cucumber continuous cropping, to study their physical properties, their effects on antioxidant enzymes of cucumber, soil enzyme, and to assess its role on alleviating continuous cropping obstacles. The results are as follows:(1) 3 strains of high PHBA-degrading ability were isolated. GLY-P1 and GLY-P2 were identified as Streptomyces griseoruber and Streptomyces canus separately, GLY-P3 was identified as Ensifer adhaerens.(2) Streptomyces griseoruber GLY-P1 and Streptomyces canus GLY-P2 have a high degradation rate at 32?C, pH10, an initial PHBA concentration of 0.5g/L. They degraded PHBA efficiently at alkaline soil. Temperature 30?C, pH7, an initial PHBA concentration of 0.5g/L, ammonium sulfate for nitrogen source and quantity of 8%(8×109) were the optimal conditions of Ensifer adhaerens GLY-P3.(3) Streptomyces griseoruber GLY-P1, Streptomyces canus GLY-P2 and Ensifer adhaerens GLY-P3 metabolize PHBA may via protocatechuic acid. The maximum productivity of protocatechuic acid by Streptomyces griseoruber GLY-P1 and Streptomyces canus GLY-P2 separately reached 3.2mg/L and 3.8mg/L at 32?C, pH7, an initial PHBA concentration of 0.5g/L in fermentation broth.(4) Under PHBA environment, SOD, CAT, DHAR and APX activities of strain Streptomyces griseoruber GLY-P1 and Streptomyces canus GLY-P2 changed compared to control, SOD, CAT, DHAR and MDHAR activities of strain Ensifer adhaerens GLY-P3 changed compared to control. This suggests when responding to PHBA, SOD, CAT, APX and DHAR may play an important part in Streptomyces griseoruber GLY-P1 and Streptomyces canus GLY-P2, SOD, CAT, MDHAR and DHAR may play an important part in strain Ensifer adhaerens GLY-P3.(5) When applied 220μg of PHBA into soil, the content of H2O2, O2.-, MDA and activities of SOD, POD, APX, DHAR were increased significantly in cucumber leaf. When inoculated GLY-P3 into the soil, the content of H2O2, O2.-, MDA and activities of SOD, CAT, POD in cucumber leaf were significantly decreased. Which suggests PHBA stress to cucumber, and GLY-P3 relieve the stress in the cucumber. Application of PHBA also changed the soil enzyme activity, inoculation of GLY-P3 reduced change of soil enzyme activity. Results showed that Ensifer adhaerens GLY-P3 can adjust the enzyme activities of itself and cucumber leaf, soil enzyme activity to relieve continuous cropping obstacle.