Interaction between 2,4-Diacetylphloroglucinol- and Hydrogen Cyanide-Producing Pseudomonas brassicacearum LBUM300 and Clavibacter michiganensis subsp. michiganensis in the Tomato Rhizosphere.

We have previously demonstrated that inoculation of tomato plants with 2,4-diacetylphloroglucinol (DAPG)- and hydrogen cyanide (HCN)-producing LBUM300 could significantly reduce bacterial canker symptoms caused by subsp. In this study, in order to better characterize the population dynamics of LBUM300 in the rhizosphere of tomato plants, we characterized the role played by DAPG and HCN production by LBUM300 on rhizosphere colonization of healthy and subsp. -infected tomato plants. The impact of subsp. presence on the expression of DAPG and HCN biosynthetic genes in the rhizosphere was also examined. assays were performed using combinations of subsp. and wild-type LBUM300 or DAPG (LBUM300Δ) or HCN (LBUM300Δ) isogenic mutant strains. Populations of LBUM300 and and gene expression levels were quantified in rhizosphere soil at several time points up to 264 h postinoculation using culture-independent quantitative PCR (qPCR) and reverse transcriptase quantitative PCR (RT-qPCR) TaqMan assays, respectively. The presence of subsp. significantly increased rhizospheric populations of LBUM300. In subsp. -infected tomato rhizospheres, the populations of wild-type LBUM300 and strain LBUM300Δ, both producing DAPG, were significantly higher than the population of strain LBUM300Δ A significant upregulation of expression was observed in the presence of subsp. , while expression was only slightly increased in the mutant strain LBUM300Δ when subsp. was present. Additionally, biofilm production was found to be significantly reduced in strain LBUM300Δ compared to the wild-type and LBUM300Δ strains. The results of this study suggest that subsp. infection of tomato plants contributes to increasing rhizospheric populations of LBUM300, a biocontrol agent, as well as the overexpression of the DAPG biosynthetic operon in this bacterium. The increasing rhizospheric populations of LBUM300 represent one of the key factors in controlling subsp. in tomato plants, as DAPG-producing bacteria have shown the ability to decrease bacterial canker symptoms in tomato plants.