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.

Keywords:

• Bacterial wilt
• nitrifying bacteria
• phytochemicals
• bioprospecting
• allyl isothiocyanate
• Molecular modeling

Acknowledgements

The authors are thankful to Director, ICAR-IARI, New Delhi for support and encouragement during the course of this investigation. A highly virulent strain of the R. solanaceraum culture provided by Dr. R. Ramesh ICAR - Central Coastal Agricultural Research Institute, Goa to verify the results obtained with that of the ITCC strain BI001 used in this study is gratefully acknowledged. This work was supported by the Indian Council of Agricultural Research-Niche Area of Excellence Programme (ICAR-NAE) (Grant number: Edn. 5(17)/2017-EP&HS), Ministry of Agriculture & Farmers Welfare, Government of India, India.

Author contribution statement

Abhishek Mandal and Anupama Singh designed the research; Abhishek Mandal, Adil Siddiqui and Amrendra Chaudhary conducted the experiments; Aditi Kundu, Anirban Dutta, Supradip Saha, Sukanta Dash and Anil Kumar analyzed the data; Abhishek Mandal, Rajesh Kumar and Veerubommu Shanmugam wrote the manuscript.

Conflict of interest

The authors declare that they have no conflict of interest.

Additional information

Funding

This work was funded by the Indian Council of Agricultural Research-Niche Area of Excellence Programme (ICAR-NAE) (Grant number: Edn. 5(17)/2017-EP&HS), Ministry of Agriculture & Farmers Welfare, Government of India, India.