Burkholderia pyrrocinia JK-SH007 is an important biocontrol strain for the prevention and treatment of poplar canker disease. Its powerful biocontrol function is inseparable from its successful colonization of poplar trees. Bacterial biofilms can ensure the long-term colonization of a host. To explore the mechanism of action of biofilms in the biocontrol process, we manipulated various exogenous factors to explore the morphology of the JK-SH007 biofilm in vitro. The addition of glycerol and MgSO 4 to TSB medium stimulated biofilm production, increased the resistance of JK-SH007 to disease, enhanced the survival of JK-SH007 in nutrient-poor environments and maintained the antagonistic ability of JK-SH007 against the poplar canker pathogen. Therefore, we constructed and optimized a biofilm-forming system to produce a large number of stable JK-SH007 biofilms. The optimized system showed that the optimal incubation time for JK-SH007 biofilm formation was 14 h, the optimal temperature of the static culture was 25 °C, and the optimal pH was 5. The optimal medium for biofilm formation was TSB medium, 1% glycerol and 50 mM MgSO 4 . RT-qPCR experiments showed that an increase in the expression of the suhB gene promoted JK-SH007 biofilm formation, while an increase in the expression level of the ropN gene inhibited JK-SH007 biofilm formation. The possible mechanism by which JK-SH007 was inhibited by biofilm formation under natural culture was revealed. These results indicate the importance of adding nutrients to JK-SH007 biocides produced on a commercial scale. This is the first report of JK-SH007 producing a long-lasting biofilm that guarantees antagonism.

Burkholderia pyrrocinia JK-SH007 is a high-potential biological control strain. We changed the composition of medium during the fermentation of JK-SH007 cells and induced these cells to form a biofilm. In this experiment, we deeply studied the biofilm physical and chemical properties. The new fermentation process improves the colonization ability of JK-SH007 and promotes poplar growth. In addition, the biofilm bacterial concentration reached 1010 CFU/mL, the cell dry weight increased over that of a control by 3-10-fold, there was increased environmental stress resistance and IAA secretion, and progeny cells retained resistance to adverse environments. The new biofilm cells were applied to poplar. The JK-SH007 colonization ability was improved in the biofilm, and some bacteria existed as biofilms (cell clusters) in poplar, which would promote forming a dominant niche. Biofilm JK-SH007 has an increased affinity for poplar during colonization and promotes poplar growth under hydroponic conditions, proving the reliability of the new morphology for treating poplar ulcer disease. This work further provides a theoretical basis for commercially producing JK-SH007.