Isolation and partial characterization of antibacterial lipopeptide produced by Paenibacillus polymyxa HKA-15 against phytopathogen Xanthomonas campestris pv. phaseoli M-5

An antibacterial metabolite was isolated from Paenibacillus polymyxa HKA-15, a soybean bacterial endophyte. The purification of the crude metabolite from Paenibacillus polymyxa HKA-15 was done by column chromatography. In TLC, a spot with an R _f value of 0.86 (±0.02) from the purified fraction showed bioactivity against Xanthomonas campestris pv. phaseoli M-5. In SDS-PAGE, the purified antibiotic was separated in the molecular weight range of 3.5 kDa. The exact molecular weight of the active compound was identified as 1,347.7 Da using MS-MS analysis. Infra red spectrum and ¹H NMR analysis showed the presence of amino acids and fatty acids in the active compound. The characterization of the antibacterial compound revealed its lipopeptide nature. In an agar diffusion assay, the crude metabolite showed a broad spectrum of activity, being able to inhibit the growth of the fungal pathogen, Rhizoctonia bataticola, Macrophomina phaseolina and Fusarium udum. A stronger inhibition was observed against bacterial pathogens viz., X. campestris pv.phaseoli M-5, X. campestris pv. phaseoli CP-1-1, Xanthomonas oryzae, Ralstonia solanacearum and Micrococcus luteus.