Antibacterial activity and mode of action of potassium tetraborate tetrahydrate against soft-rot bacterial plant pathogens

Abstract

Bacterial soft rot caused by the bacteriaDickeyaandPectobacteriumis a destructive disease of vegetables, as well as ornamental plants. Several management options exist to help control these pathogens. Because of the limited success of these approaches, there is a need for the development of alternative methods to reduce losses. In this study, we evaluated the effect of potassium tetraborate tetrahydrate (PTB) on the growth of sixDickeyaandPectobacteriumspp. Disc diffusion assays showed thatDickeyaspp. andPectobacteriumspp. differ in their sensitivity to PTB. Spontaneous PTB-resistant mutants ofPectobacteriumwere identified and further investigation of the mechanism of PTB resistance was conducted by full genome sequencing. Point mutations in genescpdBandsupKwere found in a singlePectobacterium atrosepticumPTB-resistant mutant. Additionally, point mutations in genesprfB(synonymsupK) andprmCwere found in two independentPectobacterium brasiliensePTB-resistant mutants.prfBandprmCencode peptide chain release factor 2 and its methyltransferase, respectively. We propose the disruption of translation activity due to PTB leads toPectobacteriumgrowth inhibition. TheP. atrosepticumPTB-resistant mutant showed altered swimming motility. Disease severity was reduced forP. atrosepticum-inoculated potato stems sprayed with PTB. We discuss the potential risk of selecting for bacterial resistance to this chemical.