Pea broth promotes cell motility and biocontrol activity of Lysobacter capsici AZ78 and upregulates genes related to biogenesis of type IV pili

Cells of biocontrol bacteria can colonise spaces occupied by plant pathogens by using different types of motility. In spite of the ecological importance of motility, few information is available on the motility of Lysobacter capsici. We discover that in the biocontrol bacterium L. capsici AZ78 (AZ78) motility is medium-dependent, in fact it developed dendrite-like colonies when grown on jellified pea broth (PB), while no cell movement was recorded in the media commonly used in motility assays. The application of AZ78 combined with PB increased its biocontrol activity against Plasmopara viticola under greenhouse conditions. We demonstrated that a quantity of PB equal to that present on grapevine leaves after the treatment is sufficient to determine the AZ78cell motility. To identify the molecular mechanisms involved in the medium-dependent motility, the genome of AZ78 was mined for genes responsible for the flagellum and type IV pilus (T4P) biogenesis. The subsequent gene expression analysis revealed that genes encoding structural components and regulatory factors of T4P were upregulated in AZ78 cells grown on medium containing PB, as compared with the other tested media. To the best of our knowledge, these results represent the first hint regarding the cell motility in a L. capsici biocontrol strain. Furthermore, these results pave the way to the possible role of pea compounds as coformulant, to improve the biocontrol efficacy of AZ78.