Identification of secondary metabolites biosynthetic genes, antagonistic activity and potential mechanism of <i>Bacillus subtilis</i> NBAIR-BSWG1 in suppression of <i>Alternaria alternata</i>

Abstract

Alternaria alternata wreaks havoc on fruit and vegetable production globally, threatening food security by causing black leaf spot disease. Bacillus subtilis, a natural inhabitant of soil, is a promising biological control agent for the management of A. alternata. In the present study, the antagonistic potential of B. subtilis NBAIR-BSWG1 was initially confirmed against A. alternata through a dual culture technique with 43.03% inhibition of mycelial growth. Subsequently, we extracted the cell-free extract from the NBAIR-BSWG1 pure culture and assessed its impact on A. alternata through the poison food technique and found mycelial growth inhibition of 85.82%. Identification of secondary metabolites biosynthetic genes using specific PCR markers showed the presence of surfactin genes (sfp, srf AA) with an amplicon size of 675 bp and 201 bp, respectively. Amplification of fengycin (fenB) and iturin (ituD) at 670 bp and 423 bp respectively, by using a specific PCR primer confirms the contribution of fengycin and iturin for the antagonistic potential of NBAIR-BSWG1. This study identifies NBAIR-BSWG1 as an effective bacterial biocontrol agent for control of A. alternata, unlocks the genetic basis of antifungal activity NBAIR-BSWG1, depicts molecular mechanisms involved in biological suppression of A. alternata by NBAIR-BSWG1 paving the way for the development of bioformulations for management of A. alternata.