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

Area of Science:

• Microbiology
• Biochemistry
• Agricultural Science

Background:

• Bacillus species are known producers of bioactive compounds, including cyclic lipopeptides with potential antimicrobial and insecticidal properties.
• Cyclic lipopeptides (CLPs) are amphipathic molecules with diverse biological activities, including nematicidal effects against plant-parasitic nematodes.
• Understanding the variability in CLP production and activity among different Bacillus strains is crucial for developing novel biocontrol agents.

Purpose of the Study:

• To comparatively analyze Bacillus paralicheniformis TB197 and Bacillus subtilis ATCC 21332 for their growth, cyclic lipopeptide production, and nematicidal activity.
• To characterize the specific lipopeptides responsible for nematicidal activity (NA) and determine their efficacy against Caenorhabditis elegans.
• To identify factors contributing to differences in nematicidal potency between the two Bacillus strains.

Main Methods:

• Fermentation of B. paralicheniformis TB197 and B. subtilis ATCC 21332 to obtain crude lipopeptide extracts (CLEs).
• Quantification of CLEs and assessment of nematicidal activity using the mean lethal dose (LD50) against Caenorhabditis elegans.
• Bioguided fractionation of CLEs using semipreparative thin-layer chromatography, followed by mass spectrometry for lipopeptide identification.

Main Results:

• Both strains produced comparable amounts of CLEs, but TB197 exhibited significantly higher nematicidal activity (2.1-fold) with an LD50 of 3.88 mg/mL compared to ATCC 21332's 8.15 mg/mL.
• Mass spectrometry revealed that TB197 produces fengycin A, fengycin B, surfactin, and lichenysin, while ATCC 21332 primarily produces surfactin.
• Fengycins and lichenysins from TB197 showed the highest NA (100% and 60% mortality, respectively), while surfactin from ATCC 21332 showed 63% mortality.

Conclusions:

• Bacillus paralicheniformis TB197 demonstrates superior nematicidal activity against Caenorhabditis elegans compared to Bacillus subtilis ATCC 21332.
• The enhanced activity of TB197 is attributed to its broader spectrum of lipopeptide families, particularly fengycins and lichenysins.
• More polar lipopeptides, such as fengycins, are more effective in causing mortality in C. elegans larvae, highlighting their potential as biocontrol agents.