UV-induced enhancement of rhizoviticin-dependent antagonistic activities of A. vitis VAR03-1 and electron micrograph of rhizoviticin; (A) growth inhibitory activities of the diluted filtrates prepared from the cultures of VAR03-1 (left) and its rhizoviticin-deficient mutant Δ22810 (right) with or without UV irradiation. Values represent the OD600 of each culture after 24 h of growth. Each bacterium was grown for 24 h in liquid medium, and supernatants were prepared by centrifugation and filtration; VAT03-9 (Ti) was then inoculated (initial OD600 of 0.1) and grown in supernatants serially diluted with fresh medium as indicated; data are presented as mean values and error bars represent SD (n = 3); asterisks indicate statistically significant differences from control (two-way ANOVA with Sidak’s post hoc test, P < .0001); (B) growth suppressive activities of the filtrates of UV-irradiated VAR03-1 culture at higher order dilutions; (C) relative expression levels of recA, 22810, and 22960; the VAR03-1 cells were grown in liquid medium (initial OD600 of 0.1) for 24 h and UV irradiated; cells were harvested from the cultures at 1 and 3 h after UV exposure and used for RNA preparation; as a control, the VAR03-1 cells were cultured without UV exposure; gene expression levels of each sample were measured by qRT-PCR using the relative quantification method; data are presented as mean values and error bars represent SE (n = 3); (D) electron microscopic structure of rhizoviticin in the concentrated fraction of VAR03-1 supernatants showing the highest antibiotic activity against VAT03-9 (Ti). Flexible phage tail-like structures are observed; the mean size of rhizoviticin is 164.18 ± 24.48 nm in length and 8.84 ± 0.69 nm in width (SD, n = 49); bar = 50 nm; (E) growth suppressive activities of the size (100 kDa)-fractionated culture filtrate of WT and rhizoviticin-deficient mutant of VAR03-1 against VAT03-9 (Ti) and VAR03-1 itself.