Nematicidal lipopeptides from Bacillus paralicheniformis and Bacillus subtilis: A comparative study

The aim of this work was to develop a comparative study between Bacillus paralicheniformis TB197 and B. subtilis ATCC 21332 strains in terms of growth, cyclic lipopeptide production, nematicidal activity, and active lipopeptide characteristics. Crude lipopeptide extracts (CLEs) from their fermentation broths were obtained, and their nematicidal activity (NA) was estimated as the mean lethal dose (LD₅₀), employing Caenorhabditis elegans. Using a bioguided approach, CLE components were fractionated by semipreparative thin layer chromatography, and active lipopeptides were characterized by mass spectrometry. Both strains produced similar concentrations of CLEs (p ≥ 0.05) (0.99 ± 0.11 and 1.14 ± 0.15 mg/mL by TB197 and ATCC 21332, respectively). The estimated LD₅₀ values of CLEs from the TB197 and ATCC 21332 strains were 3.88 and 8.15 mg/mL, respectively, showing that the NA of the TB197 strain CLE was 2.1-fold higher (p ≤ 0.05). Mass spectrometry revealed that strain TB197 synthesizes several families of lipopeptides, namely, fengycin A (C₁₄-C₁₇), fengycin B (C₁₆-C₁₇), surfactin (C₁₅-C₁₇), and lichenysin (C₁₂, C₁₃, C₁₄, and C₁₆), from which fengycins and lichenysins possess the highest NA (100 and 60% mortality in C. elegans larvae, respectively), while the ATCC 21332 strain produces mainly surfactin (C₁₃-C₁₇) (NA 63% mortality). The main differences found in this study were that the TB197 strain has a higher tolerance to inhibition by the product, and the lipopeptides they synthesize have a higher nematicidal activity due to the diversity of families compared to ATCC 21332. Likewise, it was shown that more polar lipopeptides (fengycins) are more effective at causing mortality in C. elegans larvae. KEY POINTS: • The nematicidal activity of lipopeptides from TB197 is higher than from ATCC 21332 • TB197 produces surfactin, lichenysin, and fengycin, while ATCC 21332 mainly produces surfactin • The most polar lipopeptides (fengycins) cause more mortality in C. elegans L2.