| Mixtures of 88 impure bacterial strains with ability of nitrogen fixation or phosphorus solubalization were inoculated to 25 media, respectively, and incubated to get mix cultures, which were inoculated to the same media and then incubated under the same condition. The procedures were repeated for 15 or 16 times, obtaining 50 stable bacterial mixture (SBM), containing two or three species in each culture. Significant growth promotion effects were observed with a half culture of 50 SBM after being inoculated to upland rice and cucumber planted in pots. Using agar plate method, 20 mixed cultures of the SBM exhibited significant growth inhibition to one ore more plant pathogens such as Verticiltiwn dahlias Kleb, Rhizoctonia solani Kiihn, Fusarium gramineanan Schw, and Pseudomonas syringae pv. lachrymans. It was found that C7 and C15 were two SBM with the most obvious antibiological effect. C7-1 and C7-4 were isolated from C7 and identified as Bacillus cereus and Pseudomonas cichorii, respectively. Neither C7-I nor C7-4 did exhibit ability to resist the plant pathogen, and the ability recovered after being mixed again. Antibiological effect was found only with C15-3, but not C15-1, however, mixture of two strains showed substancially higer antibiological ability than C15-3 isolated from SBM. Strains C15-1 and C15-3 were isolated from C15, and identified into Bacillus cereus and Paenibacillus polymyxa, respectively. It indicates synergistical action between bacterial species to form antibiological substance. The antibiological substance produced by C15-3 was found to keep the ability under conditions of pH from 2 to 9, and temperature between 30 and 80 for 30 minutes. In its components, low polar molecule would be extracted by 5 organic solvents such as Ethyl acetate, while high polar molecule remained in water phase. The substance was readily absorbed by active carbon at pH 7.5. Intensive spectrum absorption spectrum by the substance was found within wavelength from 220 nm to 300 nm, with the most intensive abosorption at 230 nm. |
