Brassica nigra essential oil: In-vitro and in-silico antibacterial efficacy against plant pathogenic and nitrifying bacteria

Abstract

The present study was aimed to examine the antibacterial potential of Brassica nigra essential oil (BNEO) against Ralstonia solanacearum, causal agent of bacterial wilt and Nitrosomonas sp., the nitrifying bacteria. In poisoned food assay, BNEO showed 100% growth inhibition of R. solancearum at ≥ 125 µg mL−1. Revalidation of findings by volatile assay employing inverted Petri plate technique exhibited 100% bacterial growth inhibition caused by vapors of BNEO, even at 50 µg mL−1 concentration. In the broth microdilution assay, the BNEO exhibited significant antibacterial activity only at higher concentrations (>500 µg mL−1). At 500 µg mL−1, BNEO showed 80% bacterial growth inhibition over control, which was at par with that of streptomycin (5 µg mL−1). In resazurin microtitre-plate assay, the maximum concentration of BNEO, at which color change occurred was 512 µg mL−1 (T9), and thus 512 µg mL−1 was concluded as the minimum inhibitory concentration (MIC). BNEO effectively inhibited the activity of Nitrosomonas spp. with 30-65% nitrification inhibition at the dose of 400 mkg−1 of Urea-N. Homology modeled protein targets assisted computational tool-based novel analysis helped to understand that the antibacterial potency of BNEO is due to preferable binding efficiency of allyl isothiocyanate (AITC), the major active ingredient of BNEO.