Co-production of a UV-stable bacteriocin-like inhibitory substance (BLIS) and indole-3-acetic acid hormone (IAA) and their optimization by Taguchi design in Bacillus pumilus

Abstract

Among 21 different nitrogen-fixing Bacillus isolates obtained from soil, 6 exhibited co-production of indole-3-acetic acid (IAA) and bacteriocin-like inhibitory substance (BLIS). One of these isolates was identified as Bacillus pumilus based on its phenotypical and biochemical properties as well as its 16S rRNA gene sequence; this isolate yielded 5.6 mg/biomass IAA co-production along with a potent BLIS production. The antimicrobial activity and proteinaceous nature of this BLIS were confirmed, and it was identified as a novel <25 kDa UV-stable peptide by SDS-PAGE. The partially purified BLIS was active against a broad range of food-borne, hospital pathogenic and spoilage bacteria, including Listeria monocytogenes , Bacillus cereus , methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococcus (VRE). In addition, it showed ideal physico-chemical properties in terms of ultraviolet and thermal resistance, water solubility, and stability against acid/alkali (pH 2.0–9.0) treatment. Finally, the effects of different variables, such as physical parameters and key media components, on determining the optimal condition of BLIS and IAA production were investigated using the Taguchi method. The co-production of a UV-stable BLIS—the first report for this isolate—and IAA demonstrate the prospective multilateral application of this Bacillus pumilus isolate as a biofertilizer and probiotic.