Quantification of antifungal lipopeptide gene expression levels in Bacillus subtilis B1 during antagonism against sapstain fungus on rubberwood

• Antibiosis plays an important role in L. theobromae inhibition.
• Surfactin lipopeptide helps in the easy movement and spreading of B. subtilis.
• Constantly expressed fengycin lipopeptide controls the sapstain growth.
• Bacilysin gene expressed in fourth and fifth days compliments sapstain inhibition.

The aesthetic value of the rubberwood is lost due to the bluish black discolouration caused by sapstain fungus, Lasiodiplodia theobromae, which leads to an economic loss in the wood industry. In our earlier study, Bacillus subtilis B1 has been identified as the potential biocontrol agent against L. theobromae, the dominant sapstain fungus infecting the rubberwood. Bacillus subtilis is known for its biocontrol activity against a wide range of fungal pathogens by various means including the action of non-ribosomal antifungal lipopeptides viz. iturin, surfactin and fengycin. The present study aims to characterize and quantify the gene expression levels of these antifungal lipopeptidic genes using RT-qPCR during inhibition process in the dual culture. Among the three lipopeptide genes, fengycin biosynthetic gene was constantly expressed in high amounts throughout the antagonism. The gene for surfactin biosynthesis was also expressed all through and may have helped in the growth and spreading of B. subtilis ​B1. Bacilysin biosynthetic gene expressed only in the fourth and fifth days dual culture might have complemented the action of fengycin in inhibiting the sapstain fungus.

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