Antagonistic Interactions Between Dickeya solani and Bacillus subtilis

Microorganisms in their natural ecological niches are constantly challenged by other inhabitants. Antagonisms exhibited by interacting microbial species are directed towards survival and increasing of their fitness. The Soft Rot Pectobacteriaceae (SRP) is a good model to study these complex microbial interactions. Along with being present in various environments, SRPs are often transferred between environments, allowing the bacteria to encounter members of other species. In this study, we investigated interactions between Dickeya solani, a representative of SRPs and a causative agent of potato soft rot, and Bacillus subtilis, which is known to be a potent producer of secondary metabolites mediating antibiosis. We have found that the soil isolate B. subtilis MB73/2 not only suppresses in vitro soft-rotting of infected potato tubers but is also able to cause directional, coordinated escape of natural isolates D. solani IFB0102 and IPO2222. While this coordinated movement of D. solani depends on surfactin produced by B. subtilis MB73/2, we show that both Dickeya strains exhibit different antagonistic interaction phenotypes toward the competing Bacillus. We prove that this antagonism depends on a single nucleotide polymorphism in one of transcriptional regulators of D. solani belonging to the LysR family.