Impact of biocontrol agents Pseudomonas fluorescens 2P24 and CPF10 on the bacterial community in the cucumber rhizosphere

Pseudomonas fluorescens 2P24 and CPF10 are two biocontrol agents that were isolated from suppressive soils of wheat take-all disease in Shandong province, China. The main objective of this study was to assess how these strains impact the bacterial community in cucumber rhizosphere in the field over 56 days. Classical microbiological culturing and molecular tools based on denaturing gradient gel electrophoresis (DGGE) and terminal-restriction fragment length polymorphism (T-RFLP) were used in this study. The survival of P. fluorescens 2P24 and CPF10 in cucumber rhizosphere was monitored by using selective plating. The results showed that the concentration of P. fluorescens 2P24 and CPF10 decreased from ca. 107 CFU/g to ca.103 CFU/g in soil after inoculation. The compared data of T-RFLP and DGGE showed temporary changes in the bacterial community in the soil that was treated with the biocontrol agents. From the 7th to 42nd days after inoculation, the alterations of several specific bacterial groups (Cyanobacterium, Beta-proteobacterium, Staphylococcus, and Bacillus) were detected in the results of DGGE with cloning and sequencing. However, on the 56th day after inoculation, there was no prominent alteration of bacterial community. In general, effects of these two biocontrol agents on indigenous bacteria in cucumber rhizosphere were transient and generally similar.